Hi
I want some help to anderstand this code specially Initialise the LCD [LCD commands] >>watch the numbers in red how do we choose them??

I tried it on the board but nothing was displayed on the LCD what is the problem??



;LCD text demo - 4 bit mode
;Nigel Goodwin 2002

LIST p=16F876A ;tell assembler what chip we are using
include "P16F876A.inc" ;include the defaults for the chip
ERRORLEVEL 0, -302 ;suppress bank selection messages
__config 0x3F11 ;sets the configuration settings (oscillator type etc.)




cblock 0x20 ;start of general purpose registers
count ;used in looping routines
count1 ;used in delay routine
counta ;used in delay routine
countb ;used in delay routine
tmp1 ;temporary storage
tmp2
templcd ;temp store for 4 bit mode
templcd2
d1
d2
endc

LCD_PORT Equ PORTB
LCD_TRIS Equ TRISB
LCD_RS Equ 0x04 ;LCD handshake lines
LCD_RW Equ 0x06
LCD_E Equ 0x07

org 0x0000

goto Initialise

Text addwf PCL, f
retlw 'H'
retlw 'e'
retlw 'l'
retlw 'l'
retlw 'o'
retlw 0x00

Text2 ADDWF PCL, f
RETLW 'R'
RETLW 'e'
RETLW 'a'
RETLW 'd'
RETLW 'y'
RETLW '.'
RETLW '.'
RETLW '.'
RETLW 0x00


Initialise clrf count
clrf PORTA
clrf PORTB

clrf PORTC


SetPorts bsf STATUS, RP0 ;select bank 1
movlw 0x00 ;make all pins outputs
movwf LCD_TRIS

MOVWF TRISC

movlw 0x07
movwf CMCON ;turn comparators off (make it like a 16F84)
bcf STATUS, RP0 ;select bank 0

call Delay100 ;wait for LCD to settle


call LCD_Init ;setup LCD

CALL LED
CALL LED
CALL LED
CALL LED

clrf count ;set counter register to zero
Message movf count, w ;put counter value in W
call Text ;get a character from the text table
xorlw 0x00 ;is it a zero?
btfsc STATUS, Z
goto NextMessage
call LCD_Char
call Delay250
incf count, f
goto Message

NextMessage call LCD_Line2 ;move to 2nd row, first column

clrf count ;set counter register to zero
Message2 movf count, w ;put counter value in W
call Text2 ;get a character from the text table
xorlw 0x00 ;is it a zero?
btfsc STATUS, Z
goto EndMessage
call LCD_Char
incf count, f
goto Message2

EndMessage

Stop goto Stop ;endless loop




;Subroutines and text tables

;LCD routines

;Initialise LCD
LCD_Init movlw 0x20 ;Set 4 bit mode
call LCD_Cmd

movlw 0x28 ;Set display shift
call LCD_Cmd

movlw 0x06 ;Set display character mode
call LCD_Cmd

movlw 0x0d ;Set display on/off and cursor command
call LCD_Cmd

call LCD_Clr ;clear display

retlw 0x00

; command set routine
LCD_Cmd movwf templcd
swapf templcd, w ;send upper nibble
andlw 0x0f ;clear upper 4 bits of W
movwf LCD_PORT
bcf PORTC, LCD_RS ;RS line to 0
call Pulse_e ;Pulse the E line high

movf templcd, w ;send lower nibble
andlw 0x0f ;clear upper 4 bits of W
movwf LCD_PORT
bcf PORTC, LCD_RS ;RS line to 0
call Pulse_e ;Pulse the E line high
call Delay5
retlw 0x00

LCD_CharD addlw 0x30
LCD_Char movwf templcd
swapf templcd, w ;send upper nibble
andlw 0x0f ;clear upper 4 bits of W
movwf LCD_PORT
bsf PORTC, LCD_RS ;RS line to 1
call Pulse_e ;Pulse the E line high

movf templcd, w ;send lower nibble
andlw 0x0f ;clear upper 4 bits of W
movwf LCD_PORT
bsf PORTC, LCD_RS ;RS line to 1
call Pulse_e ;Pulse the E line high
call Delay5
retlw 0x00

LCD_Line1 movlw 0x80 ;move to 1st row, first column
call LCD_Cmd
retlw 0x00

LCD_Line2 movlw 0xc0 ;move to 2nd row, first column
call LCD_Cmd
retlw 0x00

LCD_Line1W addlw 0x80 ;move to 1st row, column W
call LCD_Cmd
retlw 0x00

LCD_Line2W addlw 0xc0 ;move to 2nd row, column W
call LCD_Cmd
retlw 0x00

LCD_CurOn movlw 0x0d ;Set display on/off and cursor command
call LCD_Cmd
retlw 0x00

LCD_CurOff movlw 0x0c ;Set display on/off and cursor command
call LCD_Cmd
retlw 0x00

LCD_Clr movlw 0x01 ;Clear display
call LCD_Cmd
retlw 0x00

LCD_HEX movwf tmp1
swapf tmp1, w
andlw 0x0f
call HEX_Table
call LCD_Char
movf tmp1, w
andlw 0x0f
call HEX_Table
call LCD_Char
retlw 0x00


LED BSF PORTB,7
CALL Delay250
CALL Delay250
CALL Delay250
CALL Delay250
BCF PORTB,7
CALL Delay250
CALL Delay250
CALL Delay250
CALL Delay250
RETLW 0X00
;================================================= =====
Delay250 ;250ms

movlw 0x4E
movwf d1
movlw 0xC4
movwf d2
Delay_0
decfsz d1, f
goto $+2
decfsz d2, f
goto Delay_0

;3 cycles
goto $+1
nop

;4 cycles (including call)
return



Delay100
;100ms
movlw 0x1E
movwf d1
movlw 0x4F
movwf d2
Delay_1
decfsz d1, f
goto $+2
decfsz d2, f
goto Delay_1

;3 cycles
goto $+1
nop

;4 cycles (including call)
return


Delay5
;5ms
movlw 0xE6
movwf d1
movlw 0x04
movwf d2
Delay_2
decfsz d1, f
goto $+2
decfsz d2, f
goto Delay_2

;3 cycles
goto $+1
nop

;4 cycles (including call)
return







Pulse_e bsf PORTC, LCD_E
call Delay5
bcf PORTC, LCD_E
retlw 0x00

;end of LCD routines

HEX_Table ADDWF PCL , f
RETLW 0x30
RETLW 0x31
RETLW 0x32
RETLW 0x33
RETLW 0x34
RETLW 0x35
RETLW 0x36
RETLW 0x37
RETLW 0x38
RETLW 0x39
RETLW 0x41
RETLW 0x42
RETLW 0x43
RETLW 0x44
RETLW 0x45
RETLW 0x46




end



​

 

Hi zeba
I do not know the system you are having trouble with, but in general the numbers you highlight appear to be control commands for the LCD screen you have. Therefore, to specify what these should be you should have the data sheet for the LCD screen, since that is where they will come from. They aren't "to choose": they are for a particular purpose in setting the LCD up; they aren't "screen data".

THe display data appears to be in a separate routine LCD_cmd. That is what I think you need to write to the display. Like all programming for actual hardware, you need to know the details of the chip you are programming, hardware and hardware operation.

Hope this helps.

 

hi.
thanx 4 replying

I have the data sheet for the LCD and the PIC, but I didn't understand why to write 20H I mean why is is 20 not 2 or any other number??
I know it's from the data sheet but again I didn't get it I need some explain