8515 LCD Control for HD44780 (ASM)

LCD Control for mega 8515

This collection of routines writes commands and data to the Hitachi HD44780 LCD controller. Please refer to it's instruction set for a description.
PORTC is the 8 DATA lines to the LCD and PORTD pins 5-7 are the control. PORTD PIN4 is used for +5V to the LCD.

Becuase stack operations are used, this code only needs one register.
For the HD44780 LCD controller it is possible to use 4-line DATA mode, therefore saving 4 AVR pins which I will implement later.

CODE

;------------------------------------------------------------------------------------------
; LCD subroutine test

; include files
.include "m8515def.inc" ; include file for ATmega8515 AVR

; equates
.equ LCDRS = 5 ; LCD reg select pin, command/data
.equ LCDWR = 6 ; LCD read/write pin
.equ LCDCLK = 7 ; lcd clock input pin (neg clk edge)

reset:
ldi r16,high(RAMEND); stack setup
out SPH, r16 ;
ldi r16,low(RAMEND) ;
out SPL, r16 ;
ser r16 ;
out DDRC, r16 ; setup PORTC for data out
ldi r16, 0xF0 ; PORTD pin 5,6,7 for data out, pin4 for +5V
out DDRD, r16 ; to LCD
rcall lcd_init ; initialize lcd display

;*********
; main: this program simply uses lcd_cmd and lcd_prt to print "testuppr" and
; "testlowr" on a 2-line character LCD display.

main:
ldi r16, 0x00|0x80 ; place cursor in 1st row, 1st char
rcall lcd_cmd ;
ldi r16, 't'
rcall lcd_prt
ldi r16, 'e'
rcall lcd_prt
ldi r16, 's'
rcall lcd_prt
ldi r16, 't'
rcall lcd_prt
ldi r16, 'u'
rcall lcd_prt
ldi r16, 'p'
rcall lcd_prt
ldi r16, 'p'
rcall lcd_prt
ldi r16, 'r'
rcall lcd_prt

ldi r16, 0x40|0x80 ; place cursor in 2nd row, 1st char
rcall lcd_cmd ;
ldi r16, 't'
rcall lcd_prt
ldi r16, 'e'
rcall lcd_prt
ldi r16, 's'
rcall lcd_prt
ldi r16, 't'
rcall lcd_prt
ldi r16, 'l'
rcall lcd_prt
ldi r16, 'o'
rcall lcd_prt
ldi r16, 'w'
rcall lcd_prt
ldi r16, 'r'
rcall lcd_prt

end:
rjmp end

;*********************************************************************************
; lcd sub-routines

; OVERALL DESCRIPTION: This collection of routines writes commands and data
; to the Hitachi HD44780 LCD controller. Please refer to it's instruction set
; for a description.
; PORTD is the 8 DATA lines to the LCD and PORTC pins 0,3 are the control.
; For this controller it is possible to use 4-line DATA mode, saving 4 AVR pins.

;*********
lcd_init: ; lcd initialization routine
ldi r16, 0x38 ; lcd function set reg: 8 bit data lines, 5x7 font
rcall lcd_cmd ; 2 line display
ldi r16, 0x0C ; lcd display on/off reg: on, show cursor, blink
rcall lcd_cmd ;
ldi r16, 0x01 ; lcd reg: clear display, cursor home
rcall lcd_cmd ;
ldi r16, 0x06 ; lcd entry mode register: auto-increment cursor
rcall lcd_cmd ;
ret

;*********
; lcd_prt: this subroutine prints to the LCD an ascii character in r16.
; note that r16 data sent to this subroutine is lost during execution.
; This can be fixed by using stack operations on r16 before and after
; calling lcd_cmd.

lcd_prt: ; lcd write data routine (data is in r16)
sbi PORTD, LCDCLK; set lcd enable pin (simulate pos clk edge)
sbi PORTD, LCDRS; set RS to enable lcd data register
out PORTC, r16 ; put data on bus
cbi PORTD, LCDCLK; clear lcd enable (simulate neg clk edge)
rjmp lcd_wait ; go to check lcd busy flag routine
ret

;*********
; lcd_cmd: this subroutine sends instructions to the LCD from r16. These include
; everything from character placement to custom characters.
; Note r16 data sent to this subroutine is lost during execution.
; This can be fixed by using stack operations on r16 before and after
; calling lcd_cmd.

lcd_cmd: ; write command to LCD routine (command is in r16)
sbi PORTD, LCDCLK; set lcd enable pin (simulate pos clk edge)
cbi PORTD, LCDRS; clear RS to enable lcd command register
out PORTC, r16 ; put data on bus
cbi PORTD, LCDCLK; clear lcd enable (simulate neg clk edge)
rjmp lcd_wait ; go to check lcd busy flag routine
ret

;*********
; lcd_wait: because the LCD has a much slower clock than the AVR, this subroutine
; checks the LCD's busy-flag to make sure the last instruction was
; completed before continuing.
; Stack operations are used within this subroutine therefore saving
; the need for use of a second register.

lcd_wait: ; wait for lcd busy flag routine
cbi PORTD, LCDRS; clear RS to enable lcd command register
sbi PORTD, LCDWR; set RW for lcd read data enable
sbi PORTD, LCDCLK; set lcd enable pin
clr r16 ;
out DDRC, r16 ; configure data port as input
out PINC, r16 ; clear data on input pins
in r16, PINC ; get the address and busy flag
cbi PORTD, LCDCLK; clear lcd enable (simulate neg clk edge)
push r16
ser r16 ;
out DDRC, r16 ; PORTC as output again
cbi PORTD, LCDWR; clear RW again
pop r16
sbrc r16, 7 ; if busy flag cleared, return
rjmp lcd_wait ; else repeat read/check
ret