3-wire interface for standard LCD-modules
This circuit is a simple 3-wire interface for standard HD44780 and compatible LCD-text-modules.
The example code only contains parts for direct display control.
Instead of HCT164, also a LS164 can be used.
Interface schematics
Source code for Microchip PIC controller.
; Microchip PIC @ 4MHz
;------------------------------------------------------------------------
;Variblen
LCD_SERDATA ; serial daten LCD
LCD_BITCNT ; bitcounter LCD
LCD_RS ; RS flag bit 0
;------------------------------------------------------------------------
; LCD pins
#define LCD_DATA PORTB,1
#define LCD_CLK PORTB,2
#define LCD_ENABLE PORTB,3
;------------------------------------------------------------------------
;
; 8 bit to LCD plus ENABLE & RS
;
LCD_SER_SEND
movwf LCD_SERDATA
bcf LCD_ENABLE
bcf LCD_DATA
movlw 0x08
movwf LCD_BITCNT
slcd1 btfsc LCD_SERDATA,7 ; highbit data
bsf LCD_DATA
bsf LCD_CLK ; clock pulse
bcf LCD_CLK
bcf LCD_DATA
rlf LCD_SERDATA,f ; rotate left
decfsz LCD_BITCNT,f ; 8 bit ready ?
goto slcd
btfsc LCD_RS,0
bsf LCD_DATA ; rs high
nop
bs LCD_ENABLE
nop
bcf LCD_ENABLE
return
Source code for Atmel AVR controller.
; AVR @ 4MHz
.equ lcd_e = 0
.equ lcd_cl = 1
.equ lcd_da_rs = 2
.equ lcd_port = PORTC
.equ lcd_pddr = DDRC
.def loop_cnt_1 = r19 ; loop counter
.def loop_cnt_2 = r20 ; help
.def lcd_data = r22 ; daten fr lcddisplay
;***************************************************************************
;*
;* func: lcd_out_c
;* lcd_out_d
;*
;* vars: lcd_data
;* loop_cnt_1
;*
;* subs: wait_x_100u
;*
;***************************************************************************
lcd_out_c:
push loop_cnt_1
delay_x_100u 2
rcall lcd_out8
cbi lcd_port,lcd_da_rs
rjmp lcd_en
lcd_out_d:
push loop_cnt_1
delay_x_100u 2
rcall lcd_out8
sbi lcd_port,lcd_da_rs
rjmp lcd_en
lcd_en:
sbi lcd_port,lcd_e
pop loop_cnt_1
cbi lcd_port,lcd_e
ret
lcd_out8:
ldi loop_cnt_1,8
rorloop: rol lcd_data
brcs eout
cbi lcd_port,lcd_da_rs
rjmp edo
eout: sbi lcd_port,lcd_da_rs
edo: sbi lcd_port,lcd_cl
cbi lcd_port,lcd_cl
dec loop_cnt_1
brne rorloop
ret
;***************************************************************************
;*
;* func: wait_x_100u
;*
;* vars: loop_cnt_1
;* loop_cnt_2
;*
;***************************************************************************
wait_x_100u:
push loop_cnt_2
mov loop_cnt_2,loop_cnt_1
l2loop: ldi loop_cnt_1,199 ; 99
lcloop: dec loop_cnt_1
or loop_cnt_1,loop_cnt_1
brne lcloop
dec loop_cnt_2
or loop_cnt_2,loop_cnt_2
brne l2loop
pop loop_cnt_2
ret
