MSP430 Teaching Materials

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1 MSP430 Teaching Materials Capítulo 7 Comunicaciones Introducción Texas Instruments Incorporated University of Beira Interior (PT) Pedro Dinis Gaspar, António Espírito Santo, Bruno Ribeiro, Humberto Santos University of Beira Interior, Electromechanical Engineering Department Contents Introduction Communications system model Transmission mode Serial communications Synchronous and asynchronous serial communications Peripheral Interface Serial (SPI) protocol I 2 C (Inter-Integrated Circuit) protocol MSP430 communications interfaces Quiz 2 1

2 15/01/2013 Introduction Una característica importante de los sistemas basados en microprocesadores modernos es su capacidad de comunicación, es decir, su capacidad para intercambiar información con otros sistemas en el medio ambiente circundante; A bajo nivel, las interfaces de comunicación se utilizan para descargar una actualización de firmware o para establecer las configuraciones locales (por ejemplo, características encender o apagar), entre otras tareas; En un nivel superior, interfaces de comunicación se utilizan para intercambiar información en aplicaciones distribuidas. 3 Communications system model (1/2) Dispositivos de comunicación digital: Transmisor: Tiene la tarea de poner la información en el formato adecuado para su posterior transmisión; Receptor: Es el encargado de recoger el mensaje que se ha enviado y extraer la información original; Medio de comunicación: El medio físico a través del cual fluye la información y se implementa habitualmente como: Par de cable trenzado; Cable de fibra óptica; Transmisión por radiofrecuencia. 4 2

3 Communications system model (2/2) Dispositivos de un sistema de comunicación digital: DTE: Data Terminal Equipment; DCE: Data Communications Equipment. Transmitter Receiver DTE DCE Transmission medium DCE DTE Receiver Transmitter 5 Transmission mode (1/5) La comunicaciones entre dispositivos digitales pueden ser divididos en dos tiempos: Comunicaciones paralelas; Comunicaciones seriales. Comunicaciones paralelas: El medio físico de transmisión tiene líneas independientes de señal en un número igual a los bits de la palabra digital transmitida; La información transmitida en cualquier instante dado, es la palabra de datos formada por los niveles lógicos en las líneas de señal diferentes. 6 3

4 Transmission mode (2/5) Comunicaciones paralelas: Ejemplo: Carácter ASCII W en una transmisión paralela. Flujo de la información 7 Transmission mode (3/5) Comunicación serial: El medio físico de transmisión sólo necesita una línea de señal; La información transmitida es proporcionada por el transmisor como una secuencia de bits, enviado a la razón establecida entre el transmisor y el receptor; Se necesita información adicional para permitir la sincronización entre el receptor y el transmisor: Bit de inicio: se añade al inicio de la información transmitida, de modo que el receptor puede identificar el inicio de una nueva transmisión; Bit de paro(s): Añadido a la final de la información transmitida para indicar que el valor de los datos se ha completado. 8 4

5 Transmission mode (4/5) Comunicación serial: Ejemplo: Carácter ASCII W de transmisión serial: 9 Transmission mode (5/5) Ventajas y desventajas de las comunicaciones seriales y paralelas: Característica Paralela Serial Bus line One line per bit One line Sequence Transmission rate All bits of one word simultaneously High Sequence of bits Low Bus length Short distances Short and long distances Cost High Low Critical characteristics Synchronisation between the different bits is demanding Asynchronous transmission needs start and stop bits Synchronous transmission needs some other synchronisation 10 5

6 Serial communications (1/3) El bit de inicio identifica el inicio de una transferencia de datos y se genera una transición de alto a bajo en el bus; Tras el bit de inicio son los bits de datos. En este ejemplo, el código ASCII para la transferencia de texto utiliza siete bits de datos; La comprobación de errores de bit (bit de paridad) se envía después de los bits de datos; Para finalizar la transmisión, uno o dos bits de parada se emiten; A partir de siete bits de datos, el mensaje completo puede utilizar uno o dos bits de paro. Si se usan ocho bits de datos, un bit de paro sólo está disponible para la transmisión. 11 Serial communications (2/3) Bit de paridad: Se utiliza para verificar la integridad de la información transmitida; El bit se agrega por el transmisor e indica si la suma total de los números "1" en el mensaje de datos es par o impar; Las transmisiones pueden ser configurados para paridad par o impar. 12 6

7 Serial communications (3/3) Ejemplo de baud rate: La transmisión de la W : El caracter usa siete bits de datos; Cuatro bits son usados para control, haciendo un total de 11 bits. Esto corresponde a 11 bauds; Si los caracteres son transmitidos a una razón de 10 caracteres por segundo, el baud rate sería: 10x11 = 1100 baud/s. 13 Synchronous and asynchronous serial communications (1/2) Las comunicaciones seriales pueden ser: Asíncrono: donde la tasa de transmisión (baud rate) está fijado por el transmisor y el receptor funcionan en la mismo baud rate de transmisión, utilizando el bit de inicio de transmisión para sincronizar el inicio de un nuevo mensaje; Síncrono: donde hay una señal de sincronización de reloj independiente conectado entre el receptor y el transmisor. Síncrono: donde hay una señal de sincronización de reloj independiente conectado entre el receptor y el transmisor. Comunicaciones síncronas: Normalmente una unidad asume el papel de maestro y uno o más de las otras unidades tomar el papel de esclavos; La señal de reloj generada por el maestro es utilizado por las unidades esclavas para transferir datos en /hacia los registros TX y RX; Es posible que un dispositivo para transmita y reciba simultáneamente. 14 7

8 Synchronous and asynchronous serial communications (2/2) Comunicaciones asíncronas: Caracterizada por la ausencia de cualquier señal de reloj de sincronización entre las unidades; La transmisión en este modo no permite la transmisión y recepción simultáneas, es decir, cuando un dispositivo transmite los otros dispositivos sólo escuchan. 15 Serial Peripheral Interface (SPI) protocol (1/2) El bus de Interfaz Serial de Periféricos (Serial Peripheral Interface SPI) es un estándar para la comunicación serial síncrona. Desarrollado por Motorola; Funciona en mod full duplex; Relación Maestro / esclavo; Las comunicaciones son Siempre iniciadas por el maestro. Bajo costo. 16 8

9 Peripheral Interface Serial (SPI) protocol (2/2) Soporta un solo maestro; Puede soportar más de un esclavo; A corta distancia entre dispositivos, por ejemplo, en una placa de circuito impreso (PCB); Se observa especial atención en la polaridad y la fase de la señal de reloj; El maestro envía los datos en un filo de reloj y lee los datos en el otro filo. Por lo tanto, se puede enviar / recibir al mismo tiempo. 17 I 2 C (Inter-Integrated Circuit) protocol (1/3) Bus serial síncrono de computadora multi maestro; Inventado por Philips semiconductores; Desarrollado con el objetivo principal de establecer vínculos entre los circuitos integrados y para conectar periféricos de baja velocidad; Basado en un dos líneas bidireccionales con compuertas de colector abierto conectadas con resistores: SDA: Serial Data; SCL: Serial clock. Los voltajes típicos usados son de +5.0 V o +3.3 V, sin embargo otros voltajes son posibles. 18 9

10 I 2 C (Inter-Integrated Circuit) protocol (2/3) Las comunicaciones son siempre iniciados y completados por el maestro, el cual es responsable de generar la señal de reloj; En aplicaciones más complejas, I2C puede funcionar en modo de multi maestro; La selección del esclavo por el maestro es realizado usando la dirección de 7 bits del esclavo destino; El maestro (en modo de transmisión) envía: Bit de inicio; La dirección de 7-bits del esclavo con el que se desea comunicar; Con un bit se determina Con un solo bit representa si desea escribir (0) o para leer (1) desde el esclavo; El esclavo de destino responde con su dirección. 19 I 2 C (Inter-Integrated Circuit) protocol (3/3) Ejemplo de un sistema de comunicación I 2 C: 20 10

11 MSP430 communications interfaces (1/2) Equipado con tres interfaces seriales: USART (Universal Synchronous/Asynchronous Receiver/Transmitter): UART mode; SPI mode; I 2 C (on F15x/ F16x only). USCI (Universal Serial Communication Interface): UART with Lin/IrDA support; SPI (Master/Slave, 3 and 4 wire modes); I 2 C (Master/Slave, up to 400 khz). USI (Universal Serial Interface): SPI (Master/Slave, 3 & 4 wire mode); I 2 C (Master/Slave, up to 400 khz). 21 MSP430 communications interfaces (2/2) Comparación entre los módulos de comunicaciones USART USCI USI UART: - Only one modulator - n/a - n/a - n/a SPI: - Only one SPI available - Master and Slave Modes - 3 and 4 Wire Modes I 2 C: (on 15x/ 16x only) - Master and Slave Modes - up to 400kbps UART: - Two modulators support n/16 timings - Auto baud rate detection - IrDA encoder & decoder - Simultaneous USCI_A and USCI_B (2 channels) SPI: - Two SPI (one on each USCI_A and USCI_B) - Master and Slave Modes - 3 and 4 Wire Modes I 2 C: - Simplified interrupt usage - Master and Slave Modes - up to 400kbps SPI: - Only one SPI available - Master and Slave Modes I 2 C: - SW state machine needed - Master and Slave Modes 22 11

12 Quiz (1/6) 1. In the parallel communication transmission mode: (a) The data is transferred more slowly; (b) Each bit of the data has its own line; (c) All of above; (d) None of above. 2. In the serial communication transmission mode: (a) The data bits arrive sequentially; (b) The digital data is transferred faster; (c) All of above; (d) None of above. 23 Quiz (2/6) 3. The serial transmission mode is the most popular digital data communications method because: (a) Higher bit transfer rates are achieved; (b) It is cheaper to implement than parallel transmission mode; (c) All of above; (d) None of above. 4. In asynchronous serial transmission communications, the frame must include: (a) Start and stop bits. (b) Parity bit. (c) All of above; (d) None of above

13 Quiz (3/6) 5. Even parity means that an additional bit is: (a) Added to the data to make the sum of the 1 bits even; (b) Subtracted from the data to make the sum of the 1 bits even; (c) All of above; (d) None of above. 6. A USART is used: (a) Only for asynchronous transmissions; (b) Only for synchronous transmissions; (c) In parallel transmission communications; (d) In serial transmission communications. 25 Quiz (4/6) 7. Synchronous communication performed between two USART requires: (a) A common clock either in the transmitter or the receiver; (b) No common clock; (c) An independent clock in the transmitter; (d) An independent clock in the receiver. 8. Asynchronous communication between two USARTs requires: (a) A common clock in the transmitter and the receiver; (b) An independent clock in the transmitter and the receiver; (c) A common clock in the transmitter or the receiver; (d) An independent clock in the transmitter or the receiver

14 Quiz (5/6) 9. I 2 C is a bus: (a) Synchronous with a master and a slave where both can be the transmitter or receiver; (b) Where the master generates the clock; (c) All of above; (d) None of above. 27 Answers: Quiz (6/6) 1. (b) Each bit of the data has its own line. 2. (a) The data bits arrive sequentially. 3. (c) All of above. 4. (c) All of above. 5. (a) Added to the data to make the sum of the 1 bits even. 6. (d) In serial transmission communications. 7. (a) A common clock either in the transmitter or the receiver. 8. (b) An independent clock in the transmitter and the receiver. 9. (d) None of above

15 29 MSP430 Teaching Materials Capítulo 7 Comunicaciones Módulo USART Texas Instruments Incorporated University of Beira Interior (PT) Pedro Dinis Gaspar, António Espírito Santo, Bruno Ribeiro, Humberto Santos University of Beira Interior, Electromechanical Engineering Department 15

16 Contents MSP430 communications interfaces USART module introduction USART operation: UART mode USART operation: SPI mode USART registers (UART and SPI modes) Quiz 31 USART module introduction (1/2) The USART (Universal Synchronous/Asynchronous Receiver/Transmitter) este módulo esta basado para comunicaciones seriales soportando comunicaciones (RS232) y asíncronas (SPI). El módulo USART esta disponible en los dispositivos 4xx: MSP430x42x y MSP430x43x: un módulo; MSP430x44x y MSP430FG461x: Dos módulos

17 USART module introduction (2/2) El soporte del USART: Modos de operación baja potencia (con auto inicio); Modo UART o SPI (I 2 C solo en F15x/ F16x); Buffer doble TX/RX; Generador de baud rate; Habilita DMA; Detección de errores. 33 USART operation: UART mode (1/13) Transmite y recibe caracteres de forma asíncrona; La sincronización de cada carácter se basa en la selección de baud rate seleccionada; El transmisor y el receptor usa la misma frecuencia de reloj que llevan el mismo baud rate; 34 17

18 USART operation: UART mode (2/13) Proceso de Inicialización / reconfiguración recomendada: Poner SWRST (BIS.B #SWRST,&UxCTL); Inicializa todos los registros del USART con SWRST = 1 (incluyendo UxCTL); Habilita el modo USART vía los SFRs Mex (URXEx y/o UTXEx); Limpia por software SWRST (BIC.B #SWRST,&UxCTL); Habilita las interrupciones (opcional) vía los SFRs Iex (URXIEx y/o UTXIEx); 35 USART operation: UART mode (3/13) El formato del carácter se especifica como sigue: Bit de inicio; Siete u ocho bits de datos; Bit de paridad impar/par; Bit de dirección (modo de bit de dirección); Uno o dos bits de paro

19 USART operation: UART mode (6/13) Detección de error automático: El supresor de Glitch previene que la USART se inicie accidentalmente; Cualquier pulso corto en UCxRXC menor al tiempo de glitch (aproximadamente 30 ns). Error de trama FE: Se activa si el bit de paro es omitido de la trama recibida; Error de paridad PE: Se pone si la paridad es diferente de la trama recibida; Error de desbordamiento OE: Se pone si UxRXBUF es sobrescrita; Condición de ruptura BRK: Se pone si todos los bits en la trama recibida =0; 37 USART operation: UART mode (7/13) Habilitado el receptor de la USART se activa el bit URXEx: El buffer del datos recibidos, UxRXBUF, contiene el carácter movido del registro de corrimiento RX después de que el carácter ha sido recibido

20 USART operation: UART mode (8/13) Habilitado el transmisor de la USART con el bit UTXEx: La transmisión es iniciado por escribir el dato a UxTXBUF; El valor del dato se mueve al registro de corrimiento del transmisor en el siguiente pulso de reloj después que éste se vacía. 39 USART operation: UART mode (9/13) Generación del Baud rate del USART : El baud rate estándar se genera con generadores de frecuencia no convencionales. El módulo USART utiliza un pre-escalador / divisor y un modulador; El bit de temporización (BITCLK) de este módulo se permite que sea más pequeño que 1/3 de la señal de reloj, BRCLK

21 USART operation: UART mode (10/13) Generación del Baud rate del USART(continuación): Bits de temporización: Implementación en dos etapas: Par el divisor BRCLK, el factor N esta dado por: BRCLK N = baudrate Su parte entera es la primera fase del bit de tiempo; Su parte fraccionaria de este factor es el modulador; La nueva definición de N esta dado por: N = UxBR n m i n i = 0 41 USART operation: UART mode (11/13) Interrupción de la USART: Un vector de interrupciones para la transmisión y un vector para la recepción: Interrupción de la UART por transmisión: La bandera de interrupción UTXIFGx se pone el transmisor para indicar que UxTXBUF está listo para aceptar otro carácter; Una petición de interrupción también se genera si UTXIEx y GIE se activan; El bit UTXIFGx se reinicia automáticamente si la solicitud de interrupción es atendida o si un carácter se escribe en UxTXBUF

22 USART operation: UART mode (12/13) Interrupción de la USART(continuación): Interrupción de la UART por recepción: La bandera de interrupción URXIFGx se pone cada vez que se recibe un carácter y se cargan en UxRXBUF; Una petición de interrupción también se genera si URXIEx y GIE se activan; URXIFGx y URXIEx se restablecen por una señal de reinicio del sistema o cuando SWRST PUC = 1; URXIFGx se reinicia automáticamente si la interrupción pendiente es atendida (cuando URXSE = 0) o cuando se lee UxRXBUF. 43 USART operation: UART mode (13/13) La facilidad de la detección del filo de inicio del receptor (URXSE bit). Deberá usarse cuando: BRCLK es la fuente del DCO; DCO esta apagado debido al modo de operación de bajo consumo

23 Ejemplo de comunicaciones seriales //*************************************************************** // MSP430G2xx3 Demo - USCI_A0, 9600 UART Echo ISR, DCO SMCLK // // Description: Echo a received character, RX ISR used. Normal mode is LPM0. // USCI_A0 RX interrupt triggers TX Echo. // Baud rate divider with 1MHz = 1MHz/9600 = ~104.2 // ACLK = n/a, MCLK = SMCLK = CALxxx_1MHZ = 1MHz // // MSP430G2xx3 // // / \ XIN - // // -- RST XOUT - // // P1.2/UCA0TXD > // N1 // P1.1/UCA0RXD < // // D. Dang // Texas Instruments Inc. // February 2011 // Built with CCS Version and IAR Embedded Workbench Version: 5.10 //************************************************************* 45 Ejemplo de comunicaciones seriales #include "msp430g2553.h" void main(void) { WDTCTL = WDTPW + WDTHOLD; // Stop WDT BCSCTL1 = CALBC1_1MHZ; // Set DCO DCOCTL = CALDCO_1MHZ; P1SEL = BIT1 + BIT2 ; // P1.1 = RXD, P1.2=TXD P1SEL2 = BIT1 + BIT2 ; // P1.1 = RXD, P1.2=TXD UCA0CTL1 = UCSSEL_2; // SMCLK UCA0BR0 = 104; // 1MHz 9600 UCA0BR1 = 0; // 1MHz 9600 UCA0MCTL = UCBRS0; // Modulation UCBRSx = 1 UCA0CTL1 &= ~UCSWRST; // **Initialize USCI state machine** IE2 = UCA0RXIE; // Enable USCI_A0 RX interrupt _BIS_SR(GIE); while(1); } // Echo back RXed character, confirm TX buffer is ready first #pragma vector=usciab0rx_vector interrupt void USCI0RX_ISR(void) { while (!(IFG2&UCA0TXIFG)); // USCI_A0 TX buffer ready? UCA0TXBUF = UCA0RXBUF; // TX -> RXed character } 46 23

24 USART operation: SPI mode (1/8) Serial data transmitted and received by multiple devices using a shared clock provided by the master; Three or four signals are used for SPI data exchange: SIMO: Slave In, Master Out; SOMI Slave Out, Master In; UCLK USART SPI clock; STE slave transmit enable (controlled by the master). 47 USART operation: SPI mode (2/8) USART initialization/re-configuration process: Set SWRST (BIS.B #SWRST,&UxCTL); Initialize all USART registers with SWRST = 1 (including UxCTL); Enable USART module via the MEx SFRs (URXEx and/or UTXEx); Clear SWRST via software (BIC.B #SWRST,&UxCTL); Enable interrupts (optional) via the IEx SFRs (URXIEx and/or UTXIEx); 48 24

25 USART operation: SPI mode (3/8) Define mode: Master or Slave; Enable SPI transmit/receive, USPIEx; State diagram of transmit enable for SPI master mode: 49 USART operation: SPI mode (4/8) Enable SPI transmit/receive, USPIEx; State diagram of transmit enable for SPI slave mode: 50 25

26 USART operation: SPI mode (5/8) Enable SPI transmit/receive, USPIEx; State diagram of receive enable for SPI master mode: 51 USART operation: SPI mode (6/8) Enable SPI transmit/receive, USPIEx; State diagram of receive enable for SPI slave mode: 52 26

27 USART operation: SPI mode (7/8) Define serial clock control: UCLK is provided by the master on the SPI bus. MM = 1: BITCLK is provided by the USART baud rate generator on the UCLK; MM = 0: USART clock is provided on the UCLK pin by the master (baud rate generator disable); The SPI receiver and transmitter operate in parallel and use the same clock source for data transfer. Define serial clock polarity (CKPL bit) and phase (CKPH bit); 53 USART operation: SPI mode (8/8) USART interrupts: One interrupt vector for transmission and one interrupt vector for reception: UART transmit interrupt operation: UTXIFGx interrupt flag is set by the transmitter to indicate that UxTXBUF is ready to accept another character; An interrupt request is generated if UTXIEx and GIE are also set; UTXIFGx is automatically reset if the interrupt request is serviced or if a character is written to UxTXBUF

28 USART registers (UART and SPI modes) (1/11) In this section, the register bit definitions are provided for both USART peripheral interfaces: Asynchronous UART mode; Synchronous SPI mode. The registers common to both modes are described simultaneously, taking into account that some of them are represented by the same mnemonic, only differentiated by the register number ( UART for UART mode and SPI for SPI mode); The registers used exclusively for one mode are presented separately. 55 USART registers (UART and SPI modes) (2/11) UxCTL, USART Control Register Mode UART PENA PEV SPB CHAR LISTEN SYNC MM SWRST SPI Unused Unused I2C (1) CHAR LISTEN SYNC MM SWRST Bit UART mode description SPI mode description 7 PENA Parity enable when PENA = 1 Parity bit is generated (UTXDx) and expected (URXDx). 6 PEV Parity select: PEV = 0 Odd parity PEV = 1 Even parity 5 SPB Stop bit select: SPB = 0 One stop bit SPB = 1 Two stop bits 4 CHAR Character length: CHAR = 0 7-bit data CHAR = 1 8-bit data 3 LISTEN Listen enable when LISTEN = 1. The transmit signal is internally fed back to the receiver. 2 SYNC Synchronous mode enable: SYNC = 0 UART mode SYNC = 1 SPI Mode 1 MM Multiprocessor mode select MM = 0 Idle-line multiprocessor protocol MM = 1 Address-bit multiprocessor protocol 0 SWRST Software reset enable: SWRST = 0 Disabled. USART reset released for operation SWRST = 1 Enabled. USART logic held in reset state U I C L S M S Unused Unused I 2 C or SPI mode select when SYNC = 1. I 2 C 2= 0 SPI mode I 2 C = 1 I 2 C mode As UART mode As UART mode As UART mode N C Master mode: MM M= 0 USART is slave MM = 1 USART is master As UART mode W R S T 56 28

29 USART registers (UART and SPI modes) (3/11) UxTCTL, USART Transmit Control Register Mode UART Unused CKPL SSELx URXSE TXWAKE Unused TXEPT SPI CKPH CKPL SSELx Unused Unused STC TXEPT Bit UART mode description SPI mode description 7 Unused CKPH 6 CKPL Clock polarity select: CKPL = 0 UCLKI = UCLK CKPL = 1 UCLKI = inverted UCLK 5-4 SSELx BRCLK source clock: SSEL1 SSEL0 = 00 UCLKI SSEL1 SSEL0 = 01 ACLK SSEL1 SSEL0 = 10 SMCLK SSEL1 SSEL0 = 11 SMCLK CKPL SSELx 3 URXSE UART receive start-edge enable when URXSE = 1 Unused 2 TXWAKE Transmitter wake: TXWAKE = 0 Next frame transmitted is data TXWAKE = 1 Next frame transmitted is an address Unused Clock polarity select: CKPL = 0 UCLKI = The inactive state is low. CKPL = 1 UCLKI = The inactive state is high. BRCLK source clock: SSEL1 SSEL0 = 00 External UCLK (slave mode only) SSEL1 SSEL0 = 01 ACLK (master mode only) SSEL1 SSEL0 = 10 SMCLK (master mode only) SSEL1 SSEL0 = 11 SMCLK (master mode only) 1 Unused STC Slave transmit control: STC = 0 4-pin SPI mode: STE enabled. STC = 1 3-pin SPI mode: STE disabled. 0 TXEPT Transmitter empty flag: TXEPT = 0 UART is transmitting data and/or data is waiting in UxTXBUF TXEPT = 1 Transmitter shift register and UxTXBUF are empty or SWRST=1 TXEPT Transmitter empty flag: TXEPT = 0 UART is transmitting data and/or data is waiting in UxTXBUF TXEPT = 1 UxTXBUF and TX shift register are empty 57 USART registers (UART and SPI modes) (4/11) UxRCTL, USART Receive Control Register Mode UART FE PE OE BRK URXEIE URXWIE RXWAKE RXERR SPI FE Unused OE Unused Unused Unused Unused Unused Bit UART mode description SPI mode description 7 FE Framing error flag: = 0 No error = 1 Character received with low stop bit Parity error flag: 6 PE = 0 No error = 1 Character received with parity error FE Master mode framing error flag: (MM = 1, STC = 0) = 0 No conflict detected = 1 Bus conflict (STE s negative edge) Unused 5 OE Overrun error flag: = 0 No error = 1 A character was transferred into UxRXBUF before the previous character was read. 4 BRK Break detect flag: = 0 No break condition = 1 Break condition occurred Receive erroneous-character interrupt-enable: 3 URXEIE = 0 Err. characters rejected = 1 Err. characters received Receive wake-up interrupt-enable: 2 URXWIE = 0 All received characters set IFG = 1 Received address characters set IFG Receive wake-up flag: 1 RXWAKE = 0 Received character is data = 1 Received character is an address Receive error flag: 0 RXERR = 0 No receive errors detected = 1 Receive error detected OE Unused Unused Unused Unused Unused As UART mode 58 29

30 USART registers (UART and SPI modes) (5/11) UxBR0, USART Baud Rate Control Register 0 Mode UART / SPI UxBR1, USART Baud Rate Control Register 1 Mode UART / SPI Bit UART mode description SPI mode description 7 UxBRx The valid baud-rate control range is 3 UxBR < 0FFFFh, where UxBR = {UxBR1+UxBR0}. Unpredictable receive/transmit timing occurs if UxBR < 3. UxBRx The baud-rate generator uses the content of {UxBR1+UxBR0} to set the baud rate. Unpredictable SPI operation occurs if UxBR < USART registers (UART and SPI modes) (6/11) UxMCTL, USART Modulation Control Register Mode UART / SPI m7 m6 m5 m4 m3 m2 m1 m0 Bit UART mode description SPI mode description 7 UxMCTL x Selects the modulation for BRCLK. UxMCTLx Not used in SPI mode and should be set to 00h. UxRXBUF, USART Receive Buffer Register Mode UART / SPI Bit UART mode description SPI mode description 7 UxRXBUFx The receive-data buffer is user accessible and contains the last received character from the receive shift register. Reading UxRXBUF resets the receiveerror bits, the RXWAKE bit, and URXIFGx. In 7-bit data mode, UxRXBUF is LSB justified and the MSB is always cleared. UxRXBUFx The receive-data buffer is user accessible and contains the last received character from the receive shift register. Reading UxRXBUF resets the OE bit and URXIFGx flag. In 7-bit data mode, UxRXBUF is LSB justified and the MSB is always cleared

31 USART registers (UART and SPI modes) (7/11) UxTXBUF, USART Transmit Buffer Register Mode UART / SPI Bit UART mode description SPI mode description 7 UxTXBUFx The transmit data buffer is user accessible and holds the data waiting to be moved into the transmit shift register and transmitted on UTXDx. Writing to the transmit data buffer clears UTXIFGx. The MSB of UxTXBUF is not used for 7-bit data and is cleared. UxTXBUFx The transmit data buffer is user accessible and contains current data to be transmitted. When seven-bit character-length is used, the data should be MSB justified before being moved into UxTXBUF. Data is transmitted MSB first. Writing to UxTXBUF clears UTXIFGx. 61 USART registers (UART and SPI modes) (8/11) ME1, Module Enable Register 1 Mode UART UTXE0 URXE0 SPI USPIE0 Bit UART mode description SPI mode description 7 UTXE0 USART0 transmit enable: UTXE0 = 0 Module not enabled UTXE0 = 1 Module enabled 6 URXE0 USART0 receive enable: URXE0 = 0 Module not enabled URXE0 = 1 Module enabled ME2, Module Enable Register 2 USPIE0 USART0 SPI enable: USPIE0 = 0 Module not enabled USPIE0 = 1 Module enabled Mode UART UTXE1 URXE1 SPI USPIE1 Bit UART mode description SPI mode description 5 UTXE1 USART1 transmit enable: UTXE1 = 0 Module not enabled UTXE1 = 1 Module enabled 4 URXE1 USART1 receive enable: URXE1 = 0 Module not enabled URXE1 = 1 Module enabled USPIE1 USART1 SPI enable: USPIE1 = 0 Module not enabled USPIE1 = 1 Module enabled 62 31

32 USART registers (UART and SPI modes) (9/11) IE1, Interrupt Enable Register 1 Mode UART / SPI UTXIE0 URXIE0 Bit UART mode description SPI mode description 7 UTXIE0 USART0 UTXIFG0 transmit interrupt enable: UTXIE0 = 0 Interrupt not enabled UTXIE0 = 1 Interrupt enabled 6 URXIE0 USART0 URXIFG0 receive interrupt enable: URXIE0 = 0 Interrupt not enabled URXIE0 = 1 Interrupt enabled IE2, Interrupt Enable Register 2 UTXIE0 URXIE0 As UART mode As UART mode Mode UART / SPI UTXIE1 URXIE1 Bit UART mode description SPI mode description 7 UTXIE1 USART1 UTXIFG1 transmit interrupt enable: UTXIE1 = 0 Interrupt not enabled UTXIE1 = 1 Interrupt enabled 6 URXIE1 USART1 URXIFG1 receive interrupt enable: URXIE1 = 0 Interrupt not enabled URXIE1 = 1 Interrupt enabled UTXIE1 URXIE1 As UART mode As UART mode 63 USART registers (UART and SPI modes) (10/11) IFG1, Interrupt Flag Register 1 Mode UART / SPI UTXIFG0 URXIFG0 Bit UART mode description SPI mode description 7 UTXIFG0 USART0 transmit interrupt flag. UTXIFG0 is set when U0TXBUF is empty. UTXIFG0 = 0 No interrupt pending UTXIFG0 = 1 Interrupt pending 6 URXIFG0 USART0 receive interrupt flag. URXIFG0 is set when U0RXBUF has received a complete character. URXIFG0 = 0 No interrupt pending URXIFG0 = 1 Interrupt pending UTXIFG0 URXIFG0 As UART mode As UART mode 64 32

33 USART registers (UART and SPI modes) (11/11) IFG2, Interrupt Flag Register 2 Mode UART / SPI UTXIFG1 URXIFG1 Bit UART mode description SPI mode description 7 UTXIFG1 USART1 transmit interrupt flag. UTXIFG1 is set when U1TXBUF is empty. UTXIFG1 = 0 No interrupt pending UTXIFG1 = 1 Interrupt pending 6 URXIFG1 USART1 receive interrupt flag. URXIFG1 is set when U1RXBUF has received a complete character. URXIFG1 = 0 No interrupt pending URXIFG1 = 1 Interrupt pending UTXIFG1 URXIFG1 As UART mode As UART mode 65 Quiz (1/5) 1. The USART supports the following communication modes: (a) UART and I 2 C; (b) SPI and I 2 C; (c) UART and SPI; (d) None of above. 2. The USART module has: (a) One SPI module; (b) Two SPI modules; (c) Three SPI modules; (d) None of the above

34 Quiz (2/5) 3. The USART: (a) Transmits and receives characters synchronously; (b) Transmits characters synchronously and receives characters asynchronously; (c) Transmits characters asynchronously and receives characters synchronously; (d) Transmits and receives characters asynchronously. 4. The USART character format is composed of: (a) {Start bit, Seven data bits, Parity bit, Stop bit}; (b) {Start bit, Eight data bits, Parity bit, Stop bits}; (c) {Start bit, Seven data bits, Parity bit, Address bit; Stop bit}; (d) Each of the above is possible. 67 Quiz (3/5) 5. The asynchronous communication formats available to the USART module are: (a) Idle-line multiprocessor communication protocol; (b) Address bit multiprocessor communication protocol; (c) All of above; (d) None of above. 6. The automatic error detection recognizes: (a) Framing, Parity, Receive Overrun and Break condition errors; (b) Framing and Parity errors; (c) Receive Overrun and Break condition errors; (d) Framing, Parity, Receive Overrun errors

35 Quiz (4/5) 7. The serial clock control in SPI mode when MM = 1 is provided by the: (a) UCLK pin on the master; (b) BITCLK USART baud rate generator on the UCLK; (c) All of above; (d) None of above. 69 Answers Quiz (5/5) 1. (c) UART and SPI. 2. (a) One SPI module. 3. (d) Transmits and receives characters asynchronously. 4. (d) Each of the above is possible. 5. (c) All of above. 6. (a) Framing, Parity, Receive Overrun and Break condition errors. 7. (b) BITCLK USART baud rate generator on the UCLK

36 MSP430 Teaching Materials Capítulo 7 Comunicaciones Módulo USCI Texas Instruments Incorporated University of Beira Interior (PT) Pedro Dinis Gaspar, António Espírito Santo, Bruno Ribeiro, Humberto Santos University of Beira Interior, Electromechanical Engineering Department Contents MSP430 communications interfaces USCI module introduction USCI operation: UART mode USCI operation: SPI mode USCI operation: I 2 C mode USCI registers: UART, SPI and I 2 C modes Lab10b: USCI echo test Quiz 72 36

37 USCI module introduction (1/3) Although supporting UART, SPI and I 2 C, the USCI (Universal Serial Communication Interface) module is a communications interface specially designed to interconnect with high-speed industrial protocols: LIN (Local interconnect Network), used for low-cost modules in cars e.g. door modules, alarms, rain-sensors; IrDA (Infrared Data Association). The USCI module is available in the following devices: MSP430F5xx; MSP430F4xx and MSP430FG41xx; MSP430F2xx. 73 USCI module introduction (2/3) The USCI module supports: Low power operating modes (with auto-start); Two individual blocks: USCI_A: UART and SPI; USCI_B: SPI and I 2 C. Double buffered TX/RX; Baud rate/bit clock generator: With auto-baud rate detect; Flexible clock source. RX glitch suppression; DMA enabled; Error detection

38 USCI module introduction (3/3) USCI block diagram: 75 USCI operation: SPI mode (1/9) Flexible interface: 3- or 4-pin SPI; 7- or 8-bit data length; Master or slave; LSB or MSB first. S/W configurable clock phase and polarity; Programmable SPI master clock; Double buffered TX/RX; Interrupt driven TX/RX (USCI_A and USCI_B share TX and RX vector); Direct Memory Address ( DMA) enabled; LPMx operation

39 USCI operation: SPI mode (2/9) USCI module: SPI mode block diagram: 77 USCI operation: SPI mode (3/9) USCI module: SPI connections: 78 39

40 USCI operation: SPI mode (4/9) Serial data transmitted and received by multiple devices using a shared clock provided by the master; Three or four signals are used for SPI data exchange: UCxSIMO: Slave in, master out; UCxSOMI: Slave out, master in; UCxCLK: USCI SPI clock; UCxSTE: Slave transmit enable: Enables a device to receive and transmit data and is controlled by the master; 4 wire master, senses conflicts with other master(s); In 4 wire slave, externally controls TX and RX. 79 USCI operation: SPI mode (5/9) USCI initialization/re-configuration process: Set UCSWRST (BIS.B #UCSWRST,&UCAxCTL1); Initialize all USCI registers with UCSWRST = 1 (including UCxCTL1); Configure ports; Clear UCSWRST via software (BIC.B #UCSWRST,&UCxCTL1); Enable interrupts (optional) via UCxRXIE and/or UCxTXIE

41 USCI operation: SPI mode (6/9) Define the character format as presented earlier; Define mode: Master or Slave; Enable SPI transmit/receive clearing the UCSWRST bit; Define serial clock control: UCxCLK is provided by the master on the SPI bus; Configure serial clock polarity and phase (UCCKPL and UCCKPH bits). 81 USCI operation: SPI mode (7/9) USCI interrupts: One interrupt vector for transmission and one interrupt vector for reception: SPI transmit interrupt operation: UCxTXIFG interrupt flag is set by the transmitter to indicate that UCxTXBUF is ready to accept another character; An interrupt request is generated if UCxTXIE and GIE are also set; UCxTXIFG is automatically reset if the interrupt request is serviced or if a character is written to UCxTXBUF

42 USCI operation: SPI mode (8/9) USCI interrupts (continued): USCI receive interrupt operation: UCxRXIFG interrupt flag is set each time a character is received and loaded into UCxRXBUF; An interrupt request is also generated if UCxRXIE and GIE are set; UCxRXIFG and UCxRXIE are reset by a system reset PUC signal or when SWRST = 1; UCxRXIFG is automatically reset if the pending interrupt is serviced (when UCSWRST = 1) or when UCxRXBUF is read. 83 USCI operation: SPI mode (9/9) USCI interrupts (continued): SPI TX interrupt: SPI RX interrupt: 84 42

43 USCI operation: I 2 C mode (1/11) The I 2 C mode supports any master or slave I 2 C- compatible device (Specification v2.1); Each I 2 C device is recognized by a unique address and can operate as either a transmitter or a receiver, as well as either the master or the slave; A master initiates a data transfer and generates the clock signal SCL; Any device addressed by a master is considered a slave; Communication using the bi-directional serial data (SDA) and serial clock (SCL) pins; 85 USCI operation: I 2 C mode (2/11) I 2 C mode block diagram: 86 43

44 USCI operation: I 2 C mode (3/11) I 2 C mode block diagram: 87 USCI operation: I 2 C mode (4/11) Initialized using the sequence given earlier; I 2 C serial data: One clock pulse is generated by the master for each data bit transferred; Operates with byte data (MSB transferred first); The first byte after a START condition consists of a 7-bit slave address and the R/W bit: R/W = 0: Master transmits data to a slave; R/W = 1: Master receives data from a slave. The ACK bit is sent from the receiver after each byte on the 9th SCL clock

45 USCI operation: I 2 C mode (5/11) I 2 C addressing modes (7-bit and 10-bit addressing modes); I 2 C module operating modes: Master transmitter; Master receiver; Slave transmitter; Slave receiver. Arbitration procedure is invoked if two or more master transmitters simultaneously start a transmission on the bus; 89 USCI operation: I 2 C mode (6/11) I 2 C Clock generation and synchronization: SCL is provided by the master on the I 2 C bus; Master mode: BITCLK is provided by the USCI bit clock generator; Slave mode: the bit clock generator is not used

46 USCI operation: I 2 C mode (7/11) I 2 C interrupts: One interrupt vector for transmission and one interrupt vector for reception; I 2 C transmit interrupt operation: UCBxTXIFG interrupt flag is set by the transmitter to indicate that UCBxTXBUF is ready to accept another character; An interrupt request is also generated if UCBxTXIE and GIE are set; UCBxTXIFG is automatically reset if a character is written to UCBxTXBUF or a NACK is received. 91 USCI operation: I 2 C mode (8/11) I 2 C interrupts (continued): I 2 C receive interrupt operation: UCBxRXIFG interrupt flag is set each time a character is received and loaded into UCxRXBUF; An interrupt request is also generated if UCBxRXIE and GIE are set; UCBxRXIFG and UCBxRXIE are reset by a system reset PUC signal or when SWRST = 1; UCxRXIFG is automatically reset when UCBxRXBUF is read

47 USCI operation: I 2 C mode (9/11) I 2 C interrupts (continued): I 2 C transmit/receive interrupt operation: 93 USCI operation: I 2 C mode (10/11) I 2 C interrupts (continued): I 2 C state change interrupt flags: Arbitration-lost, UCALIFG: Flag is set when two or more transmitters start a transmission simultaneously, or operates as master but is addressed as a slave by another master; Not-acknowledge interrupt, UCNACKIFG: Flag set when an acknowledge is expected but is not received; Start condition detected interrupt, UCSTTIFG: Flag set when the I 2 C module detects a START condition together with its own address while in slave mode; Stop condition detected interrupt, UCSTPIFG: Flag set when the I 2 C module detects a STOP condition while in slave mode

48 USCI operation: I 2 C mode (11/11) I 2 C interrupts (continued): I 2 C TX interrupt: I 2 C RX interrupt: 95 USCI registers (UART, SPI and I 2 C modes) (1/20) UCAxCTL0, USCI_Ax Control Register 0 (UART, SPI) UCBxCTL0, USCI_Bx Control Register 0 (SPI, I 2 C) Mode UART UCPEN UCPAR UCMSB UC7BIT UCSPB UCMODEx UCSYNC=0 SPI UCCKPH UCCKPL UCMSB UC7BIT UCMST UCMODEx UCSYNC=1 I2C UCA10 UCSLA10 UCMM Unused UCMST UCMODEx=11 UCSYNC=1 Bit UART mode description SPI mode description I 2 C mode description 7 UCPEN Parity enable when UCPEN = 1 UCCKPH Clock phase select: UCCKPH = 0 Data is changed on the 1st UCLK edge and captured on the next one. UCCKPH = 1 Data is captured on the 1st UCLK edge and changed on the next one. UCA10 Own addressing mode select: UCA10= 0 7-bit address UCA10= 1 10-bit address 6 UCPAR Parity select: UCPAR = 0 Odd parity UCPAR = 1 Even parity UCCKPL Clock polarity select. UCCKPL = 0 Inactive state: low. UCCKPL = 1 Inactive state: high. UCSLA10 Slave addressing mode select: UCSLA10= 0 7-bit address UCSLA10= 1 10-bit address 5 UCMSB MSB first select: UCMSB = 0 LSB first UCMSB = 1 MSB first UCMSB As UART mode UCMM Multi-master environment select: UCMM= 0 Single master UCMM= 1 Multi master 96 48

49 USCI registers (UART, SPI and I 2 C modes) (2/20) UCAxCTL0, USCI_Ax Control Register 0 (UART, SPI) UCBxCTL0, USCI_Bx Control Register 0 (SPI, I 2 C) Mode UART UCPEN UCPAR UCMSB UC7BIT UCSPB UCMODEx UCSYNC=0 SPI UCCKPH UCCKPL UCMSB UC7BIT UCMST UCMODEx UCSYNC=1 I 2 C UCA10 UCSLA10 UCMM Unused UCMST UCMODEx=11 UCSYNC=1 Bit UART mode description SPI mode description I 2 C mode description 4 UC7BIT Character length: = 0 8-bit data = 1 7-bit data UC7BIT As UART mode Unused 3 UCSPB Stop bit select: = 0 One stop bit = 1 Two stop bits UCMST Master mode: = 0 USART is slave = 1 USART is master UCMST Master mode select. = 0 Slave mode = 1 Master mode 2-1 UCMODEx USCI asynchronous mode: = 00 UART = 01 Idle-Line Multiproc. = 10 Address-Bit Multiproc. = 11 UART with ABR. UCMODEx USCI synchronous mode: = 00 3-Pin SPI = 01 4-Pin SPI (slave enabled when UCxSTE=1) = 10 4-Pin SPI (slave enabled when UCxSTE=0) = 11 I 2 C UCMODEx=11 USCI Mode: = 00 3-Pin SPI = 01 4-Pin SPI (master/slave enabled if STE = 1) = 10 4-Pin SPI (master/slave enabled if STE = 0) = 11 I 2 C 0 UCSYNC=0 Synchronous mode enable: = 0 Asynchronous = 1 Synchronous UCSYNC=1 As UART mode UCSYNC=1 As UART mode 97 USCI registers (UART, SPI and I 2 C modes) (3/20) UCAxCTL1, USCI_Ax Control Register 1 (UART, SPI) UCBxCTL1, USCI_Bx Control Register 1 (SPI, I 2 C) Mode UART UCSSELx UCRXEIE UCBRKIE UCDORM UCTXADDR UCTXBRK UCSWRST SPI UCSSELx Unused Unused Unused Unused Unused UCSWRST I 2 C UCSSELx Unused UCTR UCTXNACK UCTXSTP UCTXSTT UCSWRST Bit UART mode description SPI mode description I 2 C mode description 7-6 UCSSELx BRCLK source clock: = 00 UCLK = 01 ACLK = 10 SMCLK = 11 SMCLK UCSSELx BRCLK source clock: = 00 N/A = 01 ACLK = 10 SMCLK = 11 SMCLK UCSSELx BRCLK source clock: = 00 UCLKI = 01 ACLK = 10 SMCLK = 11 SMCLK 5 UCRXEIE Receive erroneous-character IE: = 0 Rejected (UCAxRXIFG not set) = 1 Received (UCAxRXIFG set) 4 UCBRKIE Receive break character IE: = 0 Not set UCAxRXIFG. = 1 Set UCAxRXIFG. Unused Unused Slave addressing mode select: UCSLA10= 0 7-bit address UCSLA10= 1 10-bit address Unused UCTR Transmitter/Receiver select: = 0 Receiver = 1 Transmitter 98 49

50 USCI registers (UART, SPI and I 2 C modes) (4/20) UCAxCTL1, USCI_Ax Control Register 1 (UART, SPI) UCBxCTL1, USCI_Bx Control Register 1 (SPI, I 2 C) Mode UART UCSSELx UCRXEIE UCBRKIE UCDORM UCTXADDR UCTXBRK UCSWRST SPI UCSSELx Unused Unused Unused Unused Unused UCSWRST I 2 C UCSSELx Unused UCTR UCTXNACK UCTXSTP UCTXSTT UCSWRST Bit UART mode description SPI mode description I 2 C mode description 3 UCDORM Dormant. Puts USCI into sleep mode: = 0 Not dormant = 1 Dormant 2 UCTXADDR Transmit address: = 0 Next frame transmitted is data = 1 Next frame transmitted is address 1 UCTXBRK Transmit break: = 0 Next frame transmitted is not a break = 1 Next frame transmitted is a break or a break/synch 0 UCSWRST Software reset enable =0 Disabled. USCI reset released for operation 1 Enabled. USCI logic held in reset state Unused UCTXNACK Transmit a NACK: = 0 Acknowledge normally = 1 Generate NACK Unused UCTXSTP Transmit STOP condition in master mode: = 0 No STOP generated = 1 Generate STOP Unused UCTXSTT Transmit START condition in master mode: = 0 No START generated = 1 Generate START UCSWRST As UART mode UCSWRST As UART mode 99 USCI registers (UART, SPI and I 2 C modes) (5/20) UCAxBR0, USCI_Ax Baud Rate Control Register 0 (UART, SPI) UCBxBR0, USCI_Bx Bit Rate Control Register 0 (SPI, I 2 C) Mode UART / SPI / I 2 C UCBRx low byte UCAxBR1, USCI_Ax Baud Rate Control Register 1 (UART, SPI) UCBxBR1, USCI_Bx Bit Rate Control Register 1 (SPI, I 2 C) Mode UART / SPI / I 2 C UCBRx high byte Bit UART mode description SPI mode description I 2 C mode description 7-6 UCBRx Clock prescaler setting of the baud rate generator: Prescaler value (16-bit value) = {UCAxBR0+UCAxBR1x256} UCBRx Bit clock prescaler setting: Prescaler value (16-bit value) = {UCAxBR0+UCAxBR1 256} UCBRx As SPI mode

51 USCI registers (UART, SPI and I 2 C modes) (6/20) UCAxSTAT, USCI_Ax Status Register (UART, SPI) UCBxSTAT, USCI_Bx Status Register (SPI, I 2 C) Mode UART UCLISTEN UCFE UCOE UCPE UCBRK UCRXERR UCADDR UCIDLE UCBUSY SPI UCLISTEN UCFE UCOE Unused Unused Unused Unused UCBUSY I 2 C Unused UCSCLLOW UCGC UCBBUSY UCNACKIFG UCSTPIFG UCSTTIFG UCALIFG Bit UART mode description SPI mode description I 2 C mode description 7 UCLISTEN Listen enable: = 0 Disabled = 1 UCAxTXD is internally fed back to receiver 6 UCFE Framing error flag: = 0 No error = 1 Character with low stop bit 5 UCOE Overrun error flag: = 0 No error = 1 Overrun error UCLISTEN UCFE Listen enable: = 0 Disabled = 1 The transmitter output is internally fed back to receiver Framing error flag: = 0 No error = 1 Bus conflict (4w master) Unused UCSCLLOW SCL low: = 0 SCL is not held low = 1 SCL is held low UCOE As UART mode UCGC General call address received: = 0 No general call address = 1 General call address 101 USCI registers (UART, SPI and I 2 C modes) (7/20) UCAxSTAT, USCI_Ax Status Register (UART, SPI) UCBxSTAT, USCI_Bx Status Register (SPI, I 2 C) Mode UART UCLISTEN UCFE UCOE UCPE UCBRK UCRXERR UCADDR UCIDLE UCBUSY SPI UCLISTEN UCFE UCOE Unused Unused Unused Unused UCBUSY I 2 C Unused UCSCLLOW UCGC UCBBUSY UCNACKIFG UCSTPIFG UCSTTIFG UCALIFG Bit UART mode description SPI mode description I 2 C mode description 4 UCPE Parity error flag: = 0 No error = 1 Character with parity error 3 UCBRK Break detect flag: = 0 No break condition = 1 Break condition occurred 2 UCRXERR Receive error flag. = 0 No receive errors detected = 1 Receive error detected 1 UCADDR UCIDLE Address-bit multiproc. mode: = 0 Received character is data = 1 Received character is an address Idle-line multiproc. mode: = 0 No idle line detected = 1 Idle line detected 0 UCBUSY USCI busy: = 0 USCI inactive = 1 USCI transmit/receive Unused UCBBUSY Bus busy: = 0 Bus inactive = 1 Bus busy Unused UCNACKIFG NACK received interrupt flag: = 0 No interrupt pending = 1 Interrupt pending Unused UCSTPIFG Stop condition interrupt flag: = 0 No interrupt pending = 1 Interrupt pending Unused UCSTTIFG Start condition interrupt flag: = 0 No interrupt pending = 1 Interrupt pending UCBUSY UCALIFG Arbitration lost interrupt flag: = 0 No interrupt pending = 1 Interrupt pending

52 USCI registers (UART, SPI and I 2 C modes) (8/20) UCAxRXBUF, USCI_Ax Receive Buffer Register (UART, SPI) UCBxRXBUF, USCI_Bx Receive Buffer Register (SPI, I 2 C) Mode UART / SPI / I 2 C UCRXBUFx Bit UART mode description SPI mode description I 2 C mode description 7-0 UCRXBUFx The receive-data buffer is user accessible and contains the last received character from the receive shift register. Reading UCxRXBUF resets receive-error bits, UCADDR/UCIDLE bit and UCAxRXIFG. In 7-bit data mode, UCAxRXBUF is LSB justified and the MSB is always cleared. UCRXBUFx As UART mode Reading UCxRXBUF resets the receive-error bits, and UCxRXIFG UCRXBUFx As SPI mode 103 USCI registers (UART, SPI and I 2 C modes) (9/20) UCAxTXBUF, USCI_Ax Transmit Buffer Register (UART, SPI) UCBxTXBUF, USCI_Bx Transmit Buffer Register (SPI, I 2 C) Mode UART / SPI / I 2 C UCTXBUFx Bit UART mode description SPI mode description I 2 C mode description 7-0 UCTXBUFx The transmit data buffer is user accessible and holds the data waiting to be moved into the transmit shift register and transmitted on UCAxTXD. Writing to the transmit data buffer clears UCAxTXIFG. UCTXBUFx The transmit data buffer is user accessible and holds the data waiting to be moved into the transmit shift register and transmitted. Writing to the transmit data buffer clears UCxTXIFG. UCTXBUFx As SPI mode

53 USCI registers (UART, SPI and I 2 C modes) (10/20) IE2, Interrupt Enable Register 2 (UART, SPI, I 2 C) Mode UART UCA0TXIE UCA0RXIE SPI UCB0TXIE UCB0RXIE UCA0TXIE UCA0RXIE I 2 C UCB0TXIE UCB0RXIE Bit UART mode description SPI mode description I 2 C mode description 3 UCB0TXIE USCI_B0 transmit interrupt enable: = 0 Disabled = 1 Enabled 2 UCB0RXIE USCI_B0 receive interrupt enable: = 0 Disabled = 1 Enabled UCB0TXIE UCB0RXIE As SPI mode As SPI mode 1 UCA0TXIE USCI_A0 transmit interrupt enable: = 0 Disabled = 1 Enabled 0 UCA0RXIE USCI_A0 receive interrupt enable: = 0 Disabled = 1 Enabled UCA0TXIE UCA0RXIE As UART mode As UART mode 105 USCI registers (UART, SPI and I 2 C modes) (11/20) IFG2, Interrupt Flag Register 2 (UART, SPI, I 2 C) Mode UART UCA0TXIFG UCA0RXIFG SPI UCB0TXIFG UCB0RXIFG UCA0TXIFG UCA0RXIFG I 2 C UCB0TXIFG UCB0RXIFG Bit UART mode description SPI mode description I 2 C mode description 3 UCB0TXIFG USCI_B0 transmit interrupt flag: = 0 No interrupt pending = 1 Interrupt pending 2 UCB0RXIFG USCI_B0 receive interrupt flag: = 0 No interrupt pending = 1 Interrupt pending UCB0TXIFG UCB0RXIFG As SPI mode As SPI mode 1 UCA0TXIFG USCI_A0 transmit interrupt flag: = 0 No interrupt pending = 1 Interrupt pending 0 UCA0RXIFG USCI_A0 receive interrupt flag: = 0 No interrupt pending = 1 Interrupt pending UCA0TXIFG UCA0RXIFG As UART mode As UART mode

54 USCI registers (UART, SPI and I 2 C modes) (12/20) UC1IE, USCI_A1 Interrupt Enable Register (UART, SPI) UC1IE, USCI_B1 Interrupt Enable Register (SPI, I 2 C) Mode UART Unused Unused Unused Unused UCA1TXIE UCA1RXIE SPI Unused Unused Unused Unused UCB1TXIE UCB1RXIE UCA1TXIE UCA1RXIE I 2 C Unused Unused Unused Unused UCB1TXIE UCB1RXIE Bit UART mode description SPI mode description I 2 C mode description 3 UCB1TXIE USCI_B1 transmit interrupt enable: UTXIE1 = 0 Disabled UTXIE1 = 1 Enabled 2 UCB1RXIE USCI_B1 receive interrupt enable: URXIE1 = 0 Disabled URXIE1 = 1 Enabled UCB1TXIE UCB1RXIE As SPI mode As SPI mode 1 UCA1TXIE USCI_A1 transmit interrupt enable: UTXIE1 = 0 Disabled UTXIE1 = 1 Enabled UCA1TXIE As UART mode 0 UCA1RXIE USCI_A1 receive interrupt enable: URXIE1 = 0 Disabled URXIE1 = 1 Enabled UCA1RXIE As UART mode 107 USCI registers (UART, SPI and I 2 C modes) (13/20) UC1IFG, USCI_A1 Interrupt Flag Register (UART, SPI) UC1IFG, USCI_B1 Interrupt Flag Register (SPI, I 2 C) Mode UART UCA1TXIFG UCA1RXIFG SPI UCB1TXIFG UCB1RXIFG UCA1TXIFG UCA1RXIFG I 2 C UCB1TXIFG UCB1RXIFG Bit UART mode description SPI mode description I 2 C mode description 3 UCB1TXIFG USCI_B1 transmit interrupt flag: = 0 No interrupt pending = 1 Interrupt pending UCB1TXIFG As SPI mode 2 UCB1RXIFG USCI_B1 receive interrupt flag: = 0 No interrupt pending = 1 Interrupt pending UCB1RXIFG As SPI mode 1 UCA1TXIFG USCI_A1 transmit interrupt flag: = 0 No interrupt pending = 1 Interrupt pending 0 UCA1RXIFG USCI_A1 receive interrupt flag: = 0 No interrupt pending = 1 Interrupt pending UCA1TXIFG UCA1RXIFG As UART mode As UART mode

55 USCI registers (UART, SPI and I 2 C modes) (14/20) UCAxMCTL, USCI_Ax Modulation Control Register (UART) UCBRFx UCBRSx UCOS16 Bit UART mode description 7-4 UCBRFx First modulation pattern for BITCLK16 when UCOS16 = 1 (See Table 19-3 of the MSP430x4xx User s Guide) 3-1 UCBRSx Second modulation pattern for BITCLK (See Table 19-2 of the MSP430x4xx User s Guide) 0 UCOS16 Oversampling mode enabled when UCOS16 = USCI registers (UART, SPI and I 2 C modes) (15/20) UCAxIRTCTL, USCI_Ax IrDA Transmit Control Register (UART) UCIRTXPLx UCIRTXCLK UCIREN Bit UART mode description 7-2 UCIRTXPLx Transmit pulse length: t PULSE = (UCIRTXPLx + 1) / (2 x f IRTXCLK ) 1 UCIRTXCLK IrDA transmit pulse clock select: UCIRTXCLK = 0 BRCLK UCIRTXCLK = 1 BITCLK16, when UCOS16 = 1 BRCLK, otherwise 0 UCIREN IrDA encoder/decoder enable: UCIREN = 0 IrDA encoder/decoder disabled UCIREN = 1 IrDA encoder/decoder enabled

56 USCI registers (UART, SPI and I 2 C modes) (16/20) UCAxIRRCTL, USCI_Ax IrDA Receive Control Register (UART) UCIRRXFLx UCIRRXPL UCIRRXFE Bit UART mode description 7-2 UCIRRXFLx Receive filter length (minimum pulse length): t MIN = (UCIRRXFLx + 4) / (2 f IRTXCLK ) 1 UCIRRXPL IrDA receive input UCAxRXD polarity. When a light pulse is seen: UCIRRXPL = 0 IrDA transceiver delivers a high pulse UCIRRXPL = 1 IrDA transceiver delivers a low pulse 0 UCIRRXFE IrDA receive filter enabled: UCIRRXFE = 0 Disabled UCIRRXFE = 1 Enabled 111 USCI registers (UART, SPI and I 2 C modes) (17/20) UCAxABCTL, USCI_Ax Auto Baud Rate Control Register (UART) Reserved UCDELIMx UCSTOE UCBTOE Reserved UCABDEN Bit UART mode description 5-4 UCDELIMx Break/synch delimiter length: UCDELIM1 UCDELIM0 = 00 1 bit time UCDELIM1 UCDELIM0 = 01 2 bit times UCDELIM1 UCDELIM0 = 10 3 bit times UCDELIM1 UCDELIM0 = 11 4 bit times 3 UCSTOE Synch field time out error: UCSTOE = 0 No error UCSTOE = 1 Length of synch field exceeded measurable time 2 UCBTOE Break time out error: UCBTOE = 0 No error UCBTOE = 1 Length of break field exceeded 22 bit times. 0 UCABDEN Automatic baud rate detect enable: UCABDEN = 0 Baud rate detection disabled UCABDEN = 1 Baud rate detection enabled

57 USCI registers (UART, SPI and I 2 C modes) (18/20) UCBxI2COA, USCIBx I2C Own Address Register (I 2 C) UCGCEN I2COAx I2COAx Bit UART mode description 15 UCGCEN General call response enable: UCGCEN = 0 Do not respond to a general call UCGCEN = 1 Respond to a general call 9-0 I2COAx I 2 C own address (local address of the USCI_Bx I 2 C controller) Right-justified address 7-bit address Bit 6 is the MSB, Bits 9-7 are ignored. 10-bit address Bit 9 is the MSB. 113 USCI registers (UART, SPI and I 2 C modes) (19/20) UCBxI2CSA, USCI_Bx I 2 C Slave Address Register (I 2 C) I2CSAx I2CSAx Bit UART mode description 9-0 I2CSAx I 2 C slave address (slave address of the external device to be addressed by the USCI_Bx module) Only used in master mode Right-justified address 7-bit address Bit 6 is the MSB, Bits 9-7 are ignored. 10-bit address Bit 9 is the MSB

58 USCI registers (UART, SPI and I 2 C modes) (20/20) UCBxI2CIE, USCI_Bx I2C Interrupt Enable Register (I 2 C) Reserved UCNACKIE UCSTPIE UCSTTIE UCALIE Bit UART mode description 3 UCNACKIE Not-acknowledge interrupt enable: UCNACKIE = 0 Interrupt disabled UCNACKIE = 1 Interrupt enabled UCSTPIE UCSTTIE UCALIE Stop condition interrupt enable: UCSTPIE = 0 Interrupt disabled UCSTPIE = 1 Interrupt enabled Start condition interrupt enable: UCSTTIE = 0 Interrupt disabled UCSTTIE = 1 Interrupt enabled Arbitration lost interrupt enable: UCALIE = 0 Interrupt disabled UCALIE = 1 Interrupt enabled 115 Quiz (1/6) 1. The USCI module has: (a) One module; (b) Two modules; (c) Three modules; (d) None. 2. The USCI module in UART mode supports: (a) LIN; (b) IrDA; (c) All of above; (d) None of above

59 Quiz (2/6) 3. The UCMSB bit controls: (a) The direction of the data transfer; (b) Selects LSB or MSB first; (c) All of above; (d) None of above. 4. The automatic baud rate detection uses a break which is: (a) Detected when 11 or more continuous 0 s are received; (b) Detected when 4 or more continuous 0 s are received; (c) Detected when 8 or more continuous 0 s are received; (d) None. 117 Quiz (3/6) 5. The automatic baud rate detection uses a synch field which is represented by: (a) Data 022h inside a byte field; (b) Data 055h inside a byte field; (c) Data 044h inside a byte field; (d) None. 6. The USCI module in UART mode for IrDA decoding detects: (a) Low pulse; (b) High pulse; (c) All of above; (d) None

60 Quiz (4/6) 7. The baud rate can be generated using: (a) A low frequency; (b) Oversampling; (c) All of above; (d) None of above. 8. In USCI I 2 C communication, the ACK bit is sent from the receiver after: (a) Each bit on the 9th SCL clock; (b) Each byte on the 2th SCL clock; (c) Each bit on the 2th SCL clock; (d) Each byte on the 9th SCL clock. 119 Quiz (5/6) 9. The operating modes provided by the I 2 C mode are: (a) Master transmitter and Slave receiver; (b) Slave transmitter and Master receiver; (c) All of above; (d) None of above. 10. The I 2 C state change interrupt flags are: (a) Arbitration-lost and Not-acknowledge; (b) Start and stop conditions; (c) All of above; (d) None of above

61 Quiz (6/6) Answers: 1. (b) Two modules. 2. (c) All of above. 3. (c) All of above. 4. (a) Detected when 11 or more continuous 0 s are received. 5. (b) Data 055h inside a byte field. 6. (c) All of above. 7. (c) All of above. 8. (d) Each byte on the 9th SCL clock. 9. (c) All of above. 10. (c) All of above. 121 MSP430 Teaching Materials Chapter 7 Communicaciones USI Module Texas Instruments Incorporated University of Beira Interior (PT) Pedro Dinis Gaspar, António Espírito Santo, Bruno Ribeiro, Humberto Santos University of Beira Interior, Electromechanical Engineering Department 61

62 Contents MSP430 communications interfaces USI module introduction USI operation: SPI mode USI operation: I 2 C mode USI registers (SPI and I 2 C modes) Lab10b: Echo test using SPI Lab10c: Echo test using I 2 C Quiz 123 USI module introduction (1/2) The USI (Universal Serial Interface) module supports basic SPI and I 2 C synchronous serial communications; It is available in the MSP430x20xx family of devices; The USI module supports: SPI or I 2 C modes; Interrupt driven; Reduces CPU load; Flexible clock source selection

63 USI module introduction (2/2) USI block diagram: SPI mode: Programmable data length (8/16-bit shift register); MSB/LSB first. I 2 C mode: START/STOP detection; Arbitration lost detection. Interrupt driven; Reduces CPU load; Flexible clock source. 125 USI operation: SPI and I 2 C modes (1/5) Shift register and bit counter that include logic to support SPI and I 2 C communication; USISR shift register (up to 16 bits supported): Directly accessible by software; Contains the data to be transmitted/received (simultaneously); MSB or LSB first. Bit counter: Controls the number of bits transmitted/received; Counts the number of sampled bits; Sets USIIFG when the USICNTx = 0 (decrementing or writing zero to USICNTx bits); Writing USICNTx > 0 automatically clears USIIFG when USIIFGCC = 0 (automatically stops clocking after last bit)

64 USI operation: SPI and I 2 C modes (2/5) USI initialization: Reset USISWRST; Set USIPEx bits (USI function for the pin and maintains the PxIN and PxIFG functions for the pin): Port input levels can be read via the PxIN register by software; Incoming data stream can generate port interrupts on data transitions. 127 USI operation: SPI and I 2 C modes (3/5) Recommended USI initialization process: Set the USIPEx bits in the USI control register (USI function for the pin and set up the PxIN and PxIFG functions for the pin as well); Set the direction of the RX and TX shift register (MSB or LSB first) by USILSB bit; Select the mode (master or slave) by USIMTS bit; Enable or disable output data by USIOE bit; Enable USI interrupts by setting USIIE bit; Set up USI clock by configuring the USICKCTL control register; Enable USI by setting USISWRST bit; Read port input levels via the PxIN register by software; Incoming data stream will generate port interrupts on data transitions

65 USI operation: SPI and I 2 C modes (4/5) USI clock generation: Clock selection multiplexer: Internal clocks ACLK or SMCLK; External clock SCLK; USISWCLK (software clock input bit); Timer_A CAP/COM outputs. Configurable divider; Auto-stop on interrupt: USIIFG; Selectable phase and polarity. 129 USI operation: SPI and I 2 C modes (5/5) USICKPL: Selects the inactive level of the SPI clock (data latching on rising or falling edge); USICKPH: Selects the clock edge on which SDO is updated and SDI is sampled (idle high or low support). USIIFG automatically cleared and set by USICNTx; Clock stop on IFG: USIIFG and USISTTIFG

66 USI operation: SPI mode (1/2) Configure SPI mode: SPI master: USIMST = 1; USII2C = 0; Select clock source; SCLK -> output. SPI slave: USIMST = 0; USII2C = 0; SCLK -> input; Receives the clock externally from the master. USIPEx bits enable data and clock pins; Port logic functions, including interrupts as normal; Data output latched on shift clock. 131 USI operation: SPI mode (2/2) SPI interrupts: One interrupt vector associated with the USI module; One interrupt flag, USIIFG: Set when bit counter counts to zero; Generates an interrupt request when USIIE = 1; Cleared when USICNTx > 0 (USIIFGCC = 0), or directly by software; Stops clock when set

67 USI operation: I 2 C mode (1/10) Configure USI module in I 2 C mode: USII2C =1; USICKPL = 1; USICKPH = 0; I 2 C data compatibility: USILSB = 0; USI16B = 0; Enable SCL and SDA port functions: Set USIPE6 and USIPE USI operation: I 2 C mode (2/10) I 2 C master: USIMST = 1 and USII2C = 1; Select clock source (output to SCL line while USIIFG = 0). I 2 C slave: USIMST = 0; SCL is held low if USIIFG=1, USISTTIFG=1 or if USICNTx=