Communication with basic display devices

Transcription

1 Brno University of Technology Communication with basic display devices Microprocessor Techniques and Embedded Systems Lecture 6 Dr. Tomas Fryza Ver Nov-11

2 Contents Seven-segment display LCD displays

3 Contents Seven-segment display LCD displays

4 Seven-segment display A seven-segment display (SSD), or seven-segment indicator, is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot matrix displays. Seven-segment displays are widely used in digital clocks, electronic meters, basic calculators, and other electronic devices that display numerical information. PC7 PC2 PA3 PA3 PA4 PA7 A1 A6 PA2 PA5 PA0 PA4 PA7 A1 A6 PA2 PA5 PA0 Figure: Interconnection of seven-segment in laboratory; 6 symbols.

5 Control of seven-segment display Figure: Multiplexing of several seven-segment symbols [Rozum Stanislav et. al.].

6 Control of seven-segment display Figure: Multiplexing of several seven-segment symbols [Rozum Stanislav et. al.].

7 Control of seven-segment display Figure: Multiplexing of several seven-segment symbols [Rozum Stanislav et. al.].

8 Control of seven-segment display Figure: Multiplexing of several seven-segment symbols [Rozum Stanislav et. al.].

9 Control of seven-segment display Figure: Multiplexing of several seven-segment symbols [Rozum Stanislav et. al.].

10 Control of seven-segment display Figure: Multiplexing of several seven-segment symbols [Rozum Stanislav et. al.].

11 Control of seven-segment display Figure: Multiplexing of several seven-segment symbols [Rozum Stanislav et. al.].

12 Control of seven-segment display Figure: Multiplexing of several seven-segment symbols [Rozum Stanislav et. al.].

13 Control of seven-segment display Figure: Multiplexing of several seven-segment symbols [Rozum Stanislav et. al.].

14 Example of communication with seven-segment display 1 #i n c l u d e <a v r / i o. h> // i n c l u d e d e f i n i t i o n f i l e f o r Atmel MCU 2 #i n c l u d e <a v r / i n t e r r u p t. h> // i n c l u d e i n t e r r u p t r o u t i n e s 3 4 /* f u n c t i o n p r o t o t y p e s */ 5 /* show one d i g i t a t p o s i t i o n o f hundreds, tens, o r u n i t s */ 6 i n t showdigit ( unsigned char digit, unsigned char position ) ; 7 8 /* main a p p l i c a t i o n */ 9 i n t main ( v o i d ) 10 { sei ( ) ; 13 w h i l e (1) ; 14 r e t u r n (1) ; 15 } /* i n t e r r u p t s */ 18 /* i n t e r r u p t r o u t i n e f o r t i m e r / c o u n t e r 1 o v e r f l o w */ 19 ISR ( TIMER1_OVF_vect ) 20 { showdigit ( digit, position ) ; // show d i g i t a t p o s i t i o n 23 } /* f u n c t i o n s */ 26 /* show one d i g i t a t p o s i t i o n o f hundreds, tens, o r u n i t s */ 27 i n t showdigit ( unsigned char digit, unsigned char position ) 28 { 29 s w i t c h ( digit ){ // s e t i n d i v i d u a l LED segments 30 case 0 : } 33 r e t u r n (0) ; 34 }

15 Contents Seven-segment display LCD displays

16 LCD displays Displays in embedded applications: characters (mainly), graphical. Display area for character LCDs commonly has between 8 1 and 40 4 positions, with or without backlight. All LCD displays have control driver HD44780 from Hitachi; the principle of the communication with LCD is the communication with this driver. HD44780 has both instruction and character sets. Communication with LCD via data bus (8 signals: DB0 DB7) and via control bus (3 signals: RS, R/W, E): RS identifies instruction (command) or data, R/W identifies read or write operation, E enable signal. (a) (b) (c) Figure: Several LCD displays.

17 Communication between LCD and MCU There are two modes of data communications between LCD and MCU: 8-bit, or 4-bit. 8-bit mode: 8 data signals + 3 control signals. 4-bit mode: 4 data signals + 3 control signals: only upper half of LCD data pins is used: DB7 DB4, 8-bit data words have to be split into two nibls (groups of 4 bits) and they are send in two steps. Table: LCD pins description (display model MC1604 with 16 4 chars). Figure: Interconnection of LCD and MCU at development board in laboratory. Pin no. Symbol Description 1 V Power supply (GND) 2 V+ Power supply (+) 3 V0 Contrast adjust 4 RS Command data input 5 R/W Data read/write 6 E Enable signal 7-14 DB0 DB7 Data bus line 15 A Back light anode 16 C Back light cathode

18 Communication control between LCD and MCU Values (and meaning) of all control signals: RS = 0: on data bus there is an instruction what to do (i.e. clear screen, move cursor,...), RS = 1: on data bus there is data what we want to display, R/W = 0: write instructions or data to LCD, R/W = 1: read data from LCD, falling edge of E enables (starts) the communication, It is possible to save another MCU pin, when R/W = GND. Therefore, the LCD could only receiving instructions/data. All characters are displays as matrix of 5 8 pixels; character set is included in driver HD Data (characters) are stored in memory segment titled DDRAM (Display Data RAM). It is possible to define up to eight chars (address 0 7). This memory segment is titled CGRAM (Character Generator RAM). Characters with addresses (0x10 0x1F) and (0x80 0x9F) could not be display (equivalent to ASCII control values).

19 Example of signals waveforms Example Draw waveforms of all signals between LCD and MCU while instruction is written to LCD with (a) 8-bit and (b) 4-bit mode. Solution RS RS R/W D7 : 0 0xF0 R/W D7 : 4 0xF 0x0 E E (a) (b) Figure: Example of communication between LCD and MCU with: (a) 8-bit mode, (b) 4-bit mode.

20 Instruction set of driver HD44780 Table: Selected commands of HD44780 for communication with LCD. RS R/W DB7 : DB0 Description Clear screen x Move cursor to position (0,0) IS Set cursor move. I: incrementing cursor position. S: move whole display DCB Enable display/cursor. D: enable display. C: show cursor. B: cursor blinking L NFxx Set resolution. L=1(0): set 8(4)-bit mode. N=1(0): set two(one) lines of display. F=1(0): font size 5 10(5 7) cgram Set address cgram in CGRAM segment ddram Set address cgram in DDRAM segment. 1 0 data Write data to CGRAM. Show characters from address data. 1 0 data Write data to CGRAM or DDRAM memory segment. 1 1 data Read data from CGRAM. Read data from address data. 1 1 data Read data from CGRAM or DDRAM memory segment. RS = 0 instruction (commands) RS = 1 data

21 C code library for LCD communication Peter Fleury: Remq. Data pins have to be mapped to lower half of MPU port. Table: Selected functions from LCD library. Function name Description lcd init() ; Initialization of LCD display lcd clrscr() ; Clear LCD screen lcd gotoxy( 0, 2 ) ; Move cursor to new position (e.g. to 1st column, 3rd line) lcd putc( A ) ; Put char to LCD (e.g. A) lcd puts( "MPT" ) ; Put string (char succession) to LCD (e.g. MPT) lcd command( 0x40 ) ; Send 1-byte instruction to LCD (e.g. 0x40) lcd data( 0x0A ) ; Send 1-byte data to LCD (e.g. 0x0A) Other C code libraries: LCD library for Arduino: http: //extremeelectronics.co.in/avr-tutorials/using-lcd-module-with-avrs/...

22 LCD display character set (stored in driver HD44780) A B C D E F

23 LCD character set Characters are defined in matrix of 5 8 pixels. Shown pixel has value 1, hidden pixel has value 0. Each character is therefore represented by eight words (each for every line). User defined characters could be stored in CGRAM memory segment at the beginning of application. (a) 100 % 0b01110 (b) 40 % 0b b b b10001 (c) 0 % 0b b b b b b10001 Figure: User defined characters for LCD display battery charge indicator lcd_init ( ) ; // i n i t i a l i z a t i o n o f LCD d i s p l a y 3 lcd_clrscr ( ) ; // c l e a r LCD s c r e e n 4 5 lcd_command ( 0 b ) ; // s t o r e f o l l o w i n g two new symbols from a d d r e s s 0 6 lcd_data ( 0 b01110 ) ; // f i r s t l i n e o f new symbol 1 7 lcd_data ( 0 b11111 ) ; 8 lcd_data ( 0 b10001 ) ; 9 lcd_data ( 0 b10001 ) ; 10 lcd_data ( 0 b10001 ) ; 11 lcd_data ( 0 b10001 ) ; 12 lcd_data ( 0 b10001 ) ; 13 lcd_data ( 0 b11111 ) ; // l a s t l i n e o f new symbol 1