ECE251: Thursday November 10

Transcription

1 ECE251: Thursday November 10 Universal Asynchronous Receiver & Transmitter Text Chapter 22, Section 22.1 TM4C Data Sheet Section 14 A key topic but not a lab HW #7 due tomorrow Lab #7 finishes this week; due next week Lab # 8 (SSI) weeks of Nov 14 & 23; due week of Dec. 5 All labs MUST be completed/handed-in by Dec. 9 Practical #2 is week of Dec. 5 in lab. Extra Credit work due Dec. 9; report and demo Final Exam on Thursday, Dec 15, 9:40 11:40 a.m. Lecture #24 1

2 Types of Serial Communications Simplex--1 wire, 1 direction (TV, Radio, etc.) Half-Duplex--1 wire, 2 directions (Telephone) Line is switched: Protocol to determine how switched Full-Duplex--2 wires, 2 simultaneous directions Lecture #24 2

3 What does UART Mean? Universal UART is programmable. Asynchronous Sender provides NO clock signal to receivers Receive & Transmit Lecture #24 3

4 Serial Communication Terminology Clock: Defines the rate of data transfers (in Hz) Bit rate: The number of bits transmitted per second. It equals the clock signal rate (in bits/sec vs Hz) Bit time: Reciprocal of bit rate (sec) i.e. bit period Baud: Unit of bits transmitted per second. Baud = bits/sec. NRZ line code: Non-Return to Zero. Line Code describes the format used to transfer each information bit NRZ: The bit (1 or 0) is place on the transmission line for the entire bit cell: e.g.: Serial bit stream Bit data MODEM: MOdulator/DEModulator Used to turn digital signals into audio (telephone) signals and viceversa. Lecture #24 4

5 Serial Communication Terminology ASCII: American Standard Code for Information Interchange 7 bit code--all numbers + upper/lower case characters + many more E.g. h = $68 D = $44? = $3F = $20 See Appendix C on Lab page Parity Bit: Additional bit (usually most significant bit) used to detect a single error in a sequence of bits Typically done at character level: Use 8 bits to send a 7 bit ASCII character + parity May be Odd (extra bit makes entire sequence have odd # of ones) or may be Even (extra bit makes entire sequence have even # of ones) Example: What is D in an Odd Parity transmission? In Even? $44 = % % = $C4 odd $44 = % % = $44 even Lecture #24 5

6 Serial Communication Standards RS-232: Historically the most common asynchronous standard Established in 1960 By Electronic Industry Association (EIA) for interfacing between a computer and a modem. Revised in 1991and renamed: EIA-232-E. Still called RS-232. Computers and Terminals are Data Terminal Equipment Modems, Bridges, Routers, etc. are Data Communications Equipment Four aspects of standard Electrical--voltage levels, rise times, fall times, data rates, distances, Functional--function of signals Mechanical--# of pins, shape/dimensions of connectors Procedural--sequence of events for transmitting data Data Terminal Equipment Data Communications Equipment Lecture #24 6

7 Down and Dirty with RS-232 Signal levels: (large, ugly" voltages) 0 --between +3 and +25 v. (Typically +12 v) 1 --between -3 and -25 v. (Typically -12 v) Signal format: Start and Stop bit used to Synchronize signals Idle (high) Start bit 8-bit ASCII Code (least significant first) Stop bit 1 frame =1 character = 10 bit times Receiver must have a clock running at about 16X the transmitter s bit rate. At 28,800 baud, how long does it take to send TM4C12, including start and stop bits? What speed is the internal receiver clock? 6 char. x 10 bits/char 28,800 bits/sec = msec for 6 chars 28.8 KHz*16 = 460 KHz receiver clock frequency Lecture #24 7

8 UART Hardware UART = Universal Asynchronous Receiver/Transmitter It s the hardware (IC components in our processor/i/o subsystem) that is used to handle the asynchronous communications, at the heart of a modem s or computer s serial communication functionality. It performs Parallel Serial (transmit) and Serial Parallel (receive) conversion. See ECE102 It has a programmable clock generator to handle multiple data frequencies. It often has a multi-byte buffer to reduce frequency of CPU interrupts to transfer more data. Lecture #24 8

9 TM4C UART Capability 8 Separate UART systems on chip Half-duplex operation-can do both transmit and receive, but not at same time FIFO Buffers NRZ format. Baud rate selection using baud rate registers. Programmable 5 to 8 data bit (excluding parity) format. Interrupt generation capability. Receiver noise error detection. Framing error detection (If stop bit is not detected). Transmitter parity creation and receiver parity error detection. Lecture #24 9

10 UART Block Diagram Lecture #24 10

11 UART Character Frame from TM4C Data Sheet n is the TM4C UART number: 0-7 Lecture #24 11

12 Details of Character Frame Always a logic 0 One Start bit May be a logic 0 or 1 Always a logic 1 One or more Stop bits 7 bits plus parity 8 bits plus parity Least significant bit first Parity bit last Lecture #24 12

13 Transmitting 0x32 and 0x3C 104µsec 1 start bit, 1 stop bit, 8 data bits, no parity, baud rate = 9.6 Kbaud How would this change with even parity? With odd parity? With 7 data bits no parity? With even parity? With odd parity? With 2 stop bits? Can these transmissions represent ASCII? Lecture #24 13

14 UART Synchronization Understand this concept! IDLE SIGNAL-Stop Bit START Bit ECE102 State Machine Lecture #24 14

15 Practice with RS-232 Signals sec time What is the Baud rate? If I told you there is one stop bit per frame, with one starting on left side of slide, how many frames are being sent? Can you tell if this is 8 bits of data vs. 7 bits of data + parity If it s 7 bits of data + parity, what IS the parity So, can you tell which by looking at this chart? If it is 7 bits + parity, can it represent ASCII? If so, what ASCII characters are being transmitted? If it is 8 bits without parity, what are the bytes being transmitted (in order of being transmitted? From end of first stop bit to end of last stop bit above, how long does this transmission take? Other questions about this? Lecture #24 15

16 More Practice with RS-232 bit cell time Suppose baud rate is 19.2 Kbaud/sec with one stop bit per frame How long is a bit cell? What else can you tell me about this specific signal? Lecture #24 16

17 Even More Practice bit cell time We want to send 2Pi at 9.6Kbaud rate, using one stop bit per frame with even parity. What is the bit cell width? Show the signal above What clock rate should the receiver be using to decode this signal? OK, do you understand RS-232 signals well enough for a similar question on the final exam? Lecture #24 17

18 More on UART Next Lecture UART Signal Pins Transmit and Receive Baud Rate Generation TM4C Registers TM4C Setup and Operation As Time Allows USB Section 22.4 of text Chapter 18 of TM4C Data Sheet NOT a major topic in course Lecture #24 18