Assembly Programming an LCD with AVR

Colossus · Aug 23, 2009

The following assembly code is for a Mini DDS that generates sine, sawtooth, triangle and square waves. Frequency range is from 0.07 Hz up to 200 kHz or more. It allows you to control the frequency with 2 push buttons( up increases frequency by 10 and down decreases by 1).

I am attempting to add an LCD HD44780 to display the frequency but my assembly programming skills are pretty bad. I was wondering if someone could help me with the code?

Here is a link to the schematic.

Code:

;*******************************************************************
;*******************************************************************
;
;Description
;
; Poor-mans DDS Synthesizer
;
; Author = Jesper Hansen
; Target = AT90S2313
; Date   = 2001-02-15
;
;
; Extensively modified by Leon Heller
;
; 4/10/02   Modified for the Atmel AVR assembler
; 18/08/02    Modified for the ATtiny2313
; 18/08/02    RS-232 stuff removed
; 19/08/06    Timer0 interrupt used for timing
; 21/08/06   Pushbuttons for frequency up/down added
;
; PB0..7 = D/A Data out
; PD2 (pin 6) SW1 input
; PD3 (pin 7) SW2 input
; PD0 (pin 2) LED output
;
;*******************************************************************
;*******************************************************************
;
;
;
; Output frequency (using 24 bit accumulator) :
;
;   f = deltaPhase * fClock/2^24
;
;   fClock is in this case the CPU clock divided by the
;   number of cycles to output the data ( 9 cycles )
;
;   f = r24/r25/r26 * (11059200/9)/16777216
;
;   f = r24/r25/r26 * 0.073242188
;
;   fMax (theoretical) = 0.5 * fClock
;


#define Temp r16
#define Flags r18
#define Delay_count 0xFF
#define sw1 0  

;******************************************************************************
; start of code
;******************************************************************************

   .nolist
   .include "tn2313def.inc"
   .list

   .cseg

   .org 0
      rjmp   RESET
   .org 0x0005
      rjmp   TIMER1_OVF
   .org 0x0006
      rjmp   TIMER0_OVF


;******************************************************************************
; code
;******************************************************************************


RESET:
      ldi      Temp, RAMEND
      out      SPL, Temp      ; setup stack pointer

      ser      Temp            ;
      out      DDRB,Temp      ; set all PORTB bits as output
      sbi      PORTD,PD2      ; pullup on PD2 input
      sbi      PORTD,PD3      ; pullup on PD3 input
      sbi      DDRD,PD0      ; PD0 output


      ; set up Timer/Counter 0

      ldi    Temp,0x01
      out    TCCR0,Temp       ; Timer clock = system clock (no prescale)
      ldi    Temp,1<<TOV0
      out    TIFR,Temp       ; Clear TOV0/ clear pending interrupts
      ldi    Temp,1<<TOIE0
      out    TIMSK,Temp       ; Enable Timer/Counter0 Overflow Interrupt
      ldi      Temp,Delay_count
      out      TCNT0,Temp
      sei                  ; global enable interrupts
        

      ; set sinewave output as default
      
      ldi      ZH,high(2*sine)   ; setup Z pointer hi
      ldi      ZL,low(2*sine)   ; setup Z pointer lo


      ; clear accumulator

      ldi    r29,0x00      ; clear accumulator
      ldi    r28,0x00      ; clear accumulator

      ; setup adder registers      
      
      ldi    r24,0x00      ; setup adder value
      ldi    r25,0x88      ; to 1 kHz
      ldi    r26,0x08      ;
      
      
      
 

  
loop1:
      rcall   test_sw1
      sbrs   Flags,sw1
      rjmp   loop1
      rcall   up
      rjmp   loop1



  
test_sw1:
      sbic   PIND,PD2      ; SW1 pressed?
      rjmp   test1         ; no, return with flag = 0
      rcall   dly            ; debounce delay
      sbic   PIND,PD2      ; SW1 still closed?
      rjmp   test1         ; no, return with flag = 0
      sbr      Flags,sw1      ; sw1 flag <- 1
      rjmp   test2         ; return with dlaf <- 1
test1:
      cbr      Flags,sw1      ; sw1 flag <- 0
test2:
      ret


up:
      ldi      r16,10
      add      r25,r16
      ret

down:
      ldi      r16,1  
      sub      r25,r16
      
      ret

dly:
      ret
      ldi      r16,0x10
dly1:
      ldi      r17,0xFF
dly2:
      dec      r17
      brne   dly2
      dec      r16
      brne   dly1
      ret


; Timer0 overflow interrupt service routine
; r28,r29,r30 is the phase accumulator
; r24,r25,r26 is the adder value determining frequency
;

TIMER0_OVF:
      add      r28,r24      ; add value to accumulator
      adc      r29,r25  
      adc      r30,r26
      lpm               ; load byte from current table in ROM
      out      PORTB,r0   ; output byte to port
      ldi      Temp,Delay_count
      out      TCNT0,Temp
      reti


TIMER1_OVF:


      reti

;******************************************************************************
; data tables
;******************************************************************************

   ; force table to begin at 256 byte boundary

   .org 0x200

sine:      ; 256 step sinewave table
   .db   0x80,0x83,0x86,0x89,0x8c,0x8f,0x92,0x95,0x98,0x9c,0x9f,0xa2,0xa5,0xa8,0xab,0xae
   .db   0xb0,0xb3,0xb6,0xb9,0xbc,0xbf,0xc1,0xc4,0xc7,0xc9,0xcc,0xce,0xd1,0xd3,0xd5,0xd8
   .db   0xda,0xdc,0xde,0xe0,0xe2,0xe4,0xe6,0xe8,0xea,0xec,0xed,0xef,0xf0,0xf2,0xf3,0xf5
   .db   0xf6,0xf7,0xf8,0xf9,0xfa,0xfb,0xfc,0xfc,0xfd,0xfe,0xfe,0xff,0xff,0xff,0xff,0xff
   .db   0xff,0xff,0xff,0xff,0xff,0xff,0xfe,0xfe,0xfd,0xfc,0xfc,0xfb,0xfa,0xf9,0xf8,0xf7
   .db   0xf6,0xf5,0xf3,0xf2,0xf0,0xef,0xed,0xec,0xea,0xe8,0xe6,0xe4,0xe2,0xe0,0xde,0xdc
   .db   0xda,0xd8,0xd5,0xd3,0xd1,0xce,0xcc,0xc9,0xc7,0xc4,0xc1,0xbf,0xbc,0xb9,0xb6,0xb3
   .db   0xb0,0xae,0xab,0xa8,0xa5,0xa2,0x9f,0x9c,0x98,0x95,0x92,0x8f,0x8c,0x89,0x86,0x83
   .db   0x80,0x7c,0x79,0x76,0x73,0x70,0x6d,0x6a,0x67,0x63,0x60,0x5d,0x5a,0x57,0x54,0x51
   .db   0x4f,0x4c,0x49,0x46,0x43,0x40,0x3e,0x3b,0x38,0x36,0x33,0x31,0x2e,0x2c,0x2a,0x27
   .db   0x25,0x23,0x21,0x1f,0x1d,0x1b,0x19,0x17,0x15,0x13,0x12,0x10,0x0f,0x0d,0x0c,0x0a
   .db   0x09,0x08,0x07,0x06,0x05,0x04,0x03,0x03,0x02,0x01,0x01,0x00,0x00,0x00,0x00,0x00
   .db   0x00,0x00,0x00,0x00,0x00,0x00,0x01,0x01,0x02,0x03,0x03,0x04,0x05,0x06,0x07,0x08
   .db   0x09,0x0a,0x0c,0x0d,0x0f,0x10,0x12,0x13,0x15,0x17,0x19,0x1b,0x1d,0x1f,0x21,0x23
   .db   0x25,0x27,0x2a,0x2c,0x2e,0x31,0x33,0x36,0x38,0x3b,0x3e,0x40,0x43,0x46,0x49,0x4c
   .db   0x4f,0x51,0x54,0x57,0x5a,0x5d,0x60,0x63,0x67,0x6a,0x6d,0x70,0x73,0x76,0x79,0x7c

square:      ; 256 step squarewave table
   .db   0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
   .db   0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
   .db   0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
   .db   0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
   .db   0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
   .db   0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
   .db   0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
   .db   0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
   .db   0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff
   .db   0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff
   .db   0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff
   .db   0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff
   .db   0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff
   .db   0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff
   .db   0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff
   .db   0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff


;******************************************************************************
; end of file  
;******************************************************************************

Colossus · Aug 24, 2009

I made a diagram using the original PDF file, could you please let me know if the buttons and LCD are connected to the ATMEGA8 correctly?

http://onfinite.com/libraries/1515060/741.jpg

Here is the code i added to output the frequency to the LCD. AVR studio says there are a couple errors but let me know if i'm on the right track.

Code:

;*******************************************************************
;*******************************************************************

; Output frequency (using 24 bit accumulator) :
;
;   f = deltaPhase * fClock/2^24
;
;   fClock is in this case the CPU clock divided by the
;   number of cycles to output the data ( 9 cycles )
;
;   f = r24/r25/r26 * (11059200/9)/16777216
;
;   f = r24/r25/r26 * 0.073242188
;
;   fMax (theoretical) = 0.5 * fClock
;


#define Temp r16
#define Flags r18
#define Delay_count 0xFF
#define sw1 0   

;******************************************************************************
; start of code
;******************************************************************************

   .nolist
   ;.include "tn2313def.inc"
   .include "m32def.inc" ; *** 
   .list

   .equ lcden = 7 ; LCD Enable (Act as clk)
   .equ lcdrs = 6 ; LCD register select
   .equ lcdrw = 5 ; LCD read/write
   .cseg

   .org 0
      rjmp   RESET
   .org 0x0005
      rjmp   TIMER1_OVF
   .org 0x0006
      rjmp   TIMER0_OVF


;******************************************************************************
; code
;******************************************************************************

RESET:


      ldi      Temp, RAMEND
      out      SPL, Temp      ; setup stack pointer

      ser      Temp           ;
      out      DDRB,Temp      ; set all PORTB bits as output
      sbi      PORTD,PD2      ; pullup on PD2 input
      sbi      PORTD,PD3      ; pullup on PD3 input
      sbi      DDRD,PD0       ; PD0 output


      ; set up Timer/Counter 0

      ldi    Temp,0x01
      out    TCCR0,Temp       ; Timer clock = system clock (no prescale)
      ldi    Temp,1<<TOV0
      out    TIFR,Temp       ; Clear TOV0/ clear pending interrupts
      ldi    Temp,1<<TOIE0
      out    TIMSK,Temp       ; Enable Timer/Counter0 Overflow Interrupt
      ldi    Temp,Delay_count
      out    TCNT0,Temp
      sei                  ; global enable interrupts
         

      ; set sinewave output as default
      
      ldi      ZH,high(2*sine)   ; setup Z pointer hi
      ldi      ZL,low(2*sine)   ; setup Z pointer lo


      ; clear accumulator

      ldi    r29,0x00      ; clear accumulator
      ldi    r28,0x00      ; clear accumulator

      ; setup adder registers      
      
      ldi    r24,0x00      ; setup adder value
      ldi    r25,0x88      ; to 1 kHz
      ldi    r26,0x08      ;
      
    ;*** LCD Reset ***
 	ldi r16, low (ramend) ;Stack setup
 	out spl, r16
 	ldi r16, high (ramend)
 	out sph, r16

 	ser r16
 	out DDRD,r16        ; Setup port D as output for data
    ldi r16, 0b11100000
 	out DDRC,r16        ; Setup port C for ctrl
 	rcall lcd_init      ; Call to LCD initialization
      


; *** Output Freqencuy to LCD ***
;  run calculation every time the frequency changes, 
;  and output the number to the LCD
;  f = r24/r25/r26 * 0.073242188

main:


 	  ldi      r16,0x00     ; place cursor in 1st row, 1st char
      rcall    lcd_cmd
  
      add      r28,r24      ; Calculate f 
      adc      r29,r25   
      adc      r30,r26
      lpm                   ; load byte from current table in ROM
      out      PORTB,r0     ; output byte to port
      ldi      Temp,Delay_count
      out      TCNT0,Temp

      ldi      r16, TCNT0	; load the freq value into regester 
      rcall    lcd_prt      ; display to screen 
	  ret


loop:
 rjmp loop


;*** LCD initialization ***
lcd_init:
 ldi   r16,0x38       ;Function Set:8 bit mode & 5 x 7 dot font
 rcall lcd_cmd
 ldi   r16,0x38       ;Function Set:8 bit mode & 5 x 7 dot font
 rcall lcd_cmd
 ldi   r16,0x38       ;Function Set:8 bit mode & 5 x 7 dot font
 rcall lcd_cmd
 ldi   r16, 0x0F      ;Display on, cursor on, cursor blink
 rcall lcd_cmd
 ldi   r16, 0x06      ;auto increment cursor
 rcall lcd_cmd
 rcall main
 ret
 

;*** Send data to be displayed ***
lcd_prt:
 cbi PORTC, lcdrs ; RS=1 sending instruction
 nop
 cbi PORTC, lcdrw ; RW=0 write operation
 nop
 out PORTD,r16    ; put data on bus
 nop
 sbi PORTC, lcden ; simulate +ve clk edge
 nop
 nop
 nop
 cbi PORTC, lcden ; simulate -ve clk edge
 ret
    

;*** Send commmand to LCD ***
lcd_cmd:
 cbi PORTC, lcdrs ; RS=0 sending instruction
 nop
 cbi PORTC, lcdrw ; RW=0 write operation
 nop
 out PORTD,r16    ; put data on bus
 nop
 sbi PORTC, lcden ; simulate +ve clk edge
 nop
 nop
 nop
 cbi PORTC, lcden ; simulate -ve clk edge
 ret 



loop1:
      rcall   test_sw1
      sbrs   Flags,sw1
      rjmp   loop1
      rcall   up
      rjmp   loop1



   
test_sw1:
      sbic   PIND,PD2      ; SW1 pressed?
      rjmp   test1         ; no, return with flag = 0
      rcall  dly           ; debounce delay
      sbic   PIND,PD2      ; SW1 still closed?
      rjmp   test1         ; no, return with flag = 0
      sbr    Flags,sw1     ; sw1 flag <- 1
      rjmp   test2         ; return with dlaf <- 1
test1:
      cbr    Flags,sw1     ; sw1 flag <- 0
test2:
      ret


up:
      ldi      r16,10
      add      r25,r16
      ret

down:
      ldi      r16,1   
      sub      r25,r16
      
      ret

dly:
      ret
      ldi      r16,0x10
dly1:
      ldi      r17,0xFF
dly2:
      dec      r17
      brne    dly2
      dec      r16
      brne    dly1
      ret


; Timer0 overflow interrupt service routine
; r28,r29,r30 is the phase accumulator
; r24,r25,r26 is the adder value determining frequency
;

TIMER0_OVF:
      add      r28,r24      ; add value to accumulator
      adc      r29,r25   
      adc      r30,r26
      lpm                   ; load byte from current table in ROM
      out      PORTB,r0     ; output byte to port
      ldi      Temp,Delay_count
      out      TCNT0,Temp
      reti


TIMER1_OVF:


      reti


;******************************************************************************
; data tables
;******************************************************************************

   ; force table to begin at 256 byte boundary

   .org 0x200

square:      ; 256 step squarewave table
   .db   0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
   .db   0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
   .db   0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
   .db   0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
   .db   0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
   .db   0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
   .db   0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
   .db   0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
   .db   0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff
   .db   0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff
   .db   0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff
   .db   0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff
   .db   0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff
   .db   0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff
   .db   0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff
   .db   0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff


;******************************************************************************
; end of file   
;******************************************************************************

[/code]

Pommie · Aug 24, 2009

You are on the right track but your code and diagram don't agree with each other.

You diagram is for 4 bit data on C0-C3. You code is for 8 bit data on D0-D7.
Your diagram has the R/W line grounded, your code is using it.

The way your diagram is wired, you need 4 bit code that uses delays instead of reading the busy signal. Try here.

Mike.

Colossus · Aug 24, 2009

Thanks for the link.

As you might have guessed i'm rather new to assembly programming. That don't teach you this stuff in school and i major in computer science. There was one course, assembly level programming where we briefly used SAL/MAL/TAL to program RISC but that's about it. Everything else we learn is high level programming mainly with C/C++/Java.

So, in the code where exactly is the frequency variable stored and which of the following routines do I need to send it to the LCD?

Thanks for all your help!

Code:

; ******************************************************************
;    L C D    D I S P L A Y    D E M O
; ******************************************************************
;
;   Provides the entry point for a simple "Hello World" impelmentation
;   using my LCD routines.
;
;   Author:   Adam Swann <adam@velocity2.com>
;   Homepage: http://www.velocity2.com/~adam/
;
;   http://www.adamswann.com/projects/avr-lcd/
;
;   See LCD.asm for more information.
;
; ******************************************************************

   .nolist
   .include "8515def.inc"
   .list

   .cseg



.def    Temp      = r16
.def    Temp2      = r17

; Define generic port names (change the 'A' to whatever you're using)
.equ   LCD_PORT  = PORTC
.equ   LCD_DDR     = DDRC
.equ   LCD_PIN     = PINC

; Define the pin numbers
.equ   LCD_E       = 1
.equ   LCD_RW      = 2
.equ   LCD_RS      = 3

.def   DelayTime = r20
.equ   DelayCount1 = 128


      .org   0
      rjmp   RESET

RESET:   ldi     Temp, low(RAMEND)
       out      SPL, Temp
       ldi      Temp, high(RAMEND)
       out      SPH, temp      ; Initialize Stackpointer

      ldi     Temp, 0x00
      out     LCD_PORT, Temp      ; Clear the outputs

      ldi     Temp, 0xFF
      out     LCD_DDR, Temp       ; Set the direction to output

      ldi     DelayTime, 255      ; Set the default delay length
                  ; (see my delay.asm)

      rcall   LCD_Init

      rcall    DELAY

      ldi     r30, low(strInit1*2)
      ldi     r31, high(strInit1*2)
      ldi     Temp2,   16
      rcall   LCD_PrintPM

      ; *** Send the cursor to beginning of second line
      ldi     Temp, 0b11000000
      rcall    LCD_SendCmd

      ldi     r30, low(strInit2*2)
      ldi     r31, high(strInit2*2)
      ldi     Temp2,   16
      rcall   LCD_PrintPM


      rcall    DELAY



FOREVER:   rjmp    FOREVER

strInit1:   .db   " Hello World!   "
strInit2:   .db   "It worked!!!    "

; ******************************************************************
;    L C D    D I S P L A Y    R O U T I N E S
; ******************************************************************
;
;   Interfaces the AVR '8515 microcontroller with LCDs controlled
;   by the Samsung KS0066U (and similiar) LCD driver.
;
;   Author:   Adam Swann <adam@velocity2.com>
;   Homepage: http://www.velocity2.com/~adam/
;
;   The code below is fairly straightforward and well-documented.
;   See my Web site or e-mail me if you need further instructions.
;
;   I used an 8515 at 4 MHz.  My LCD is Jameco Part #171715.
;
;   I wired the LCD display as follows (onto Port C)
;    
;      AVR   LCD
;      0 --> no connection
;      1 --> Enable on LCD
;      2 --> R/W on LCD
;      3 --> RS on LCD
;      4 --> Data4
;      5 --> Data5
;      6 --> Data6
;      7 --> Data7 
;
;   References: (URLs may be wrapped)
;    o KS0066U Datasheet <http://www.usa.samsungsemi.com/
;                          products/summary/charlcd/ks0066u.htm>
;
; ******************************************************************

; *** LCD_Init: Routine to initialize the LCD.
LCD_Init:   push   Temp

      ldi   DelayTime, 255

      ; Put the LCD in 8-bit mode.  Even though we want the display to
      ; operate in 4-bit mode, the only way to guarantee that our commands
      ; are aligned properly is to initialize in 8-bit.  (The user might have
      ; hit reset between nibbles of a dual 4-bit cycle.)
      ldi   Temp, 0b00110000
      out   LCD_PORT, Temp
      rcall   LCD_PulseE

      rcall   DELAY
      rcall   DELAY

      ; Now it's safe to go into 4-bit mode.
      ldi   Temp, 0b00100000
      out   LCD_PORT, Temp
      rcall   LCD_PulseE

      rcall    DELAY
      rcall   DELAY

      ; *** Send the 'FUNCTION SET' command
      ;         +------ Data:  0 = 4-bit; 1 = 8-bit
      ;         |+----- Lines: 0 = 1; 1 = 2
      ;         ||+---- Font:  0 = 5x8; 1 = 5x11
      ldi   Temp, 0b00101100
      rcall    LCD_SendCmd

      ; *** Send the 'CURSOR/DISPLAY SHIFT' command
      ;          +----- S/C:  0 = cursor; 1 = display
      ;          |+---- R/L:  0 = left; 1 = right
      ldi   Temp, 0b00010100
      rcall    LCD_SendCmd

      ; *** Send the 'DISPLAY ON/OFF' command
      ;           +---- Display: 0 = off; 1 = on
      ;           |+--- Cursor: 0 = off; 1 = on
      ;           ||+-- Blink: 0 = off; 1 = on
      ldi   Temp, 0b00001100
      rcall    LCD_SendCmd

      ; *** Send the 'ENTRY MODE' command
      ;            +--- Direction: 0 = left; 1 = right
      ;            |+-- Shift Dislay: 0 = off; 1 = on
      ldi   Temp, 0b00000110
      rcall    LCD_SendCmd

      rcall    LCD_Clear

      pop    Temp
      ret

; *** LCD_PrintMem: Prints from memory.
;       Put the starting memory location in Z (r31:r30)
;       Put the number of characters to print in Temp2
;   After execution, Z is at the character AFTER the last to be printed
;                    and Temp2 is zero.
;       This function will not wrap if you the string is bigger than the LCD.

LCD_PrintMem:   push   Temp

   LCD_MemRead: ld   Temp, Z+
      rcall   LCD_SendChar
      dec   Temp2
      brne   LCD_MemRead

      pop   Temp
      ret

; *** LCD_PrintEE: Prints from EEPROM
;LCD_PrintEE:   push   Temp
;
 ;   LCD_EERead: sbic    EECR, EEWE    ; Wait for EEWE to clear
;      rjmp    LCD_EERead
;
;      out    EEARH, r31    ;output address high byte, remove if no high byte exist
;      out    EEARL, r30    ;output address low byte
;
;      sbi    EECR, EERE    ;set EEPROM Read strobe
;      in    Temp, EEDR    ;get data
;
;      rcall   LCD_SendChar
;
;      dec   Temp2
;      brne   LCD_EERead
;
;      pop   Temp
;      ret

; *** LCD_PrintPM: Prints from program memory
LCD_PrintPM:   push   r0
      push   Temp

    LCD_PMRead: lpm
          mov   Temp, r0
      rcall   LCD_SendChar
      adiw   r30, 1
      dec   Temp2
      brne   LCD_PMRead

      pop   Temp
      pop   r0
      ret



; *** LCD_Clear: Clears the display and sends the cursor home.

LCD_Clear:   push    Temp

      ; *** Clear the display
      ldi   Temp, 0b00000001
      rcall    LCD_SendCmd

      ; *** Send the cursor home
      ldi   Temp, 0b00000010
      rcall    LCD_SendCmd

      pop   Temp
      ret

; *** LCD_SendCmd: Routine to write a command to the instruction register.
;       The value to be written should be stored in Temp.
;       The value is sent 4 bits at a time.

LCD_SendCmd:   push    Temp
      push    Temp2

      rcall   LCD_WaitBusy

      mov    Temp2, Temp      ; Make a backup copy
      andi    Temp2, 0b11110000   ; Only use the upper nibble
      out   LCD_PORT, Temp2      ; Send it
      rcall    LCD_PulseE      ; Pulse the enable

      swap   Temp         ; Swap upper/lower nibble
      andi    Temp, 0b11110000   ; Only use the upper nibble
      out   LCD_PORT, Temp      ; Send it
      rcall    LCD_PulseE      ; Pulse the enable

      pop    Temp2
      pop    Temp
      ret
; *** LCD_SendChar: Routine to write a character to the data register.
;       The value to be written should be stored in Temp.
;       The value is sent 4 bits at a time.

LCD_SendChar:   push    Temp
      push    Temp2

      mov    Temp2, Temp      ; Make a backup copy
      rcall   LCD_WaitBusy
      mov    Temp, Temp2      ; Make a backup copy

      andi    Temp2, 0b11110000   ; Only use the upper nibble
      ori   Temp2,  0b00001000
      out   LCD_PORT, Temp2      ; Send it
      rcall    LCD_PulseE      ; Pulse the enable

      swap   Temp         ; Swap upper/lower nibble
      andi    Temp,  0b11110000   ; Only use the upper nibble
      ori   Temp,  0b00001000
      out   LCD_PORT, Temp      ; Send it
      rcall    LCD_PulseE      ; Pulse the enable

      pop    Temp2
      pop    Temp
      ret

; *** LCD_WaitBusy: Wait for the busy flag to go low.
;       Waits for the busy flag to go low.  Since we're in 4-bit mode,
;       the register has to be read twice (for a total of 8 bits).  The
;       second read is never used.
;       If you need more code space, this function could be replaced with
;       a simple delay.

LCD_WaitBusy:   push    Temp

      ldi   Temp, 0b00001111   ; Disable data bit outputs
      out   LCD_DDR, Temp

      ldi   Temp, 0x00      ; Clear all outputs
      out   LCD_PORT, Temp

LCDWaitLoop:   ldi   Temp, 0b00000100   ; Enable only read bit
      out   LCD_PORT, Temp
      sbi   LCD_PORT, LCD_E      ; Raise the Enable signal.
      nop
      nop
      in   Temp, LCD_PIN      ; Read the current values
      cbi   LCD_PORT, LCD_E      ; Disable the enable signal.
      rcall    LCD_PulseE      ; Pulse the enable (the second nibble is discarded)
      sbrc   Temp, 7         ; Check busy flag
      rjmp   LCDWaitLoop

      ldi   Temp, 0b11111111   ; Enable all outputs
      out   LCD_DDR, Temp

      pop   Temp
      ret

LCD_PulseE:   sbi   LCD_PORT, LCD_E
      nop
      nop
      cbi   LCD_PORT, LCD_E
      ret

; *** Provide millisecond delay (DelayTicks specifies number of ms)
DELAY:   push DelayTime
   push r25

   ldi   r25, DelayCount1

DELAY1:   dec r25
   brne DELAY1
   dec DelayTime
   brne DELAY1

   pop r25
   pop DelayTime
   ret

Colossus · Aug 25, 2009

So, I drew up a new diagram using the

**broken link removed**

Let me know if the new diagram looks okay?

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Assembly Programming an LCD with AVR

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