Hello guys,

I want to display a message "Hello" on a 16x2 LCD. I am using PIC16F877 and I am programing using assembly language. I used proteus to build or design my project. The LCD does not display the message so I would like you guys help me by looking on what is wrong to my code and my circuit.

my code

    list      p=16f877            ; list directive to define processor
 #include <p16f877.inc>        ; processor specific variable definitions
 
 __CONFIG _CP_OFF & _WDT_OFF & _BODEN_ON & _PWRTE_ON & _RC_OSC & _WRT_ENABLE_ON & _LVP_ON & _DEBUG_OFF & _CPD_OFF 
; '__CONFIG' directive is used to embed configuration data within .asm file.
; The lables following the directive are located in the respective .inc file.
; See respective data sheet for additional information on configuration word.
 
 

;***** VARIABLE DEFINITIONS
w_temp        EQU     0x7E        ; variable used for context saving 
status_temp   EQU     0x7F        ; variable used for context saving
  cblock 0x20
            count            ;used in loops
            count1   ;used in delay routine
   counta   ;used in delay routine
   countb   ;used in delay routine
            templcd ;temp store for 4 bit mode
  endc 
LCD_RS Equ 0x04 ;LCD handshake lines
;LCD_RW connected to the ground
LCD_E Equ 0x07
 

;**********************************************************************
  ORG     0x000             ; processor reset vector
  clrf    PCLATH            ; ensure page bits are cleared
    goto    Main             ; go to beginning of program

  ORG     0x004             ; interrupt vector location
  movwf   w_temp            ; save off current W register contents
  movf STATUS,w          ; move status register into W register
  movwf status_temp       ; save off contents of STATUS register

; isr code can go here or be located as a call subroutine elsewhere

  movf    status_temp,w     ; retrieve copy of STATUS register
  movwf STATUS            ; restore pre-isr STATUS register contents
  swapf   w_temp,f
  swapf   w_temp,w          ; restore pre-isr W register contents
  retfie                    ; return from interrupt
 

 
;----------------------------------------------------------------------------------------
 
;Subroutines:
Init 
        clrw                    ; Zero.
        movwf   PORTB      ;resets input/output ports
        bsf     STATUS,RP0      ; Select Bank 1
  movlw   b'00000000'    ; Set port B bits 0-3 as outputs b0-b3 connected to lcd  d4-d7 pins
                                ;and b6-b7 connected to RS,E and RW grounded       
        movwf   TRISB        ; Set TRISB register 
        bcf     STATUS,RP0      ; Select Bank 0 
       
        retlw 0
 
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

LCD_Cmd  
        movwf templcd
  swapf templcd, w ;send upper nibble
  andlw 0x0f   ;clear upper 4 bits of W
  movwf PORTB
  bcf     PORTB,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 PORTB
  bcf     PORTB,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 PORTB
  bsf     PORTB,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 PORTB
  bsf     PORTB,LCD_RS   ;RS line to 1
  call Pulse_e   ;Pulse the E line high
  call  Delay5
  retlw 0x00
LCD_Clr  
        movlw 0x01   ;Clear display
  call LCD_Cmd
  retlw 0x00
Delay255 
        movlw 0xff  ;delay 255 mS
  goto d0
Delay100
     movlw d'100'  ;delay 100mS
  goto d0
Delay50
  movlw d'50'  ;delay 50mS
  goto d0
Delay20 
     movlw d'20'  ;delay 20mS
  goto d0
Delay5
  movlw 0x05  ;delay 5.000 ms (4 MHz clock)
d0  movwf count1
d1  movlw 0xC7   ;delay 1mS
  movwf counta
  movlw 0x01
  movwf countb
Delay_0
  decfsz counta, f
  goto $+2
  decfsz countb, f
  goto Delay_0
  decfsz count1 ,f
  goto d1
  retlw 0x00
Text
  addwf PCL, f
  retlw 'H'
  retlw 'e'
  retlw 'l'
  retlw 'l'
  retlw 'o'
  retlw 0x00
Pulse_e  
        bsf PORTB,LCD_E
  nop
  bcf PORTB,LCD_E
  retlw 0x00
 

EndMessage 
  
Stop  goto Stop   ;endless loop
 

;Program Start:

  
Main 
        call Init
        call Delay100  ;wait for LCD to settle
        call   LCD_Init
        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 EndMessage
        call LCD_Char
        incf count, f
        goto message

        END

On the attachment I have the hex file and the proteus design and the picture of my circuit

 

Hello guys,

    list      p=16f877            ; list directive to define processor
 #include <p16f877.inc>        ; processor specific variable definitions
 
 __CONFIG _CP_OFF & _WDT_OFF & _BODEN_ON & _PWRTE_ON & _RC_OSC & _WRT_ENABLE_ON & _LVP_ON & _DEBUG_OFF & _CPD_OFF

As I can see you have used _RC_OSC setting in the config word. But in your circuit you use a xtal configuration. That may give you some trouble

 

I have changed it to

 list      p=16f877            ; list directive to define processor
 #include <p16f877.inc>        ; processor specific variable definitions
 
 __CONFIG _CP_OFF & _WDT_OFF & _BODEN_ON & _PWRTE_ON & _XT_OSC & _WRT_ENABLE_ON & _LVP_ON & _DEBUG_OFF & _CPD_OFF

Still there was no text displayed

 

Your LCD initialisation routine seems to be lacking some steps and is missing critical delays between instructions.
Get the relevant data sheet for your LCD display controller and follow the suggested initialisation sequence to the letter paying particular attention to the delays that must occur between instructions during the early steps of initialisation.

 

Timing is critical in LCD displays. Then setting it up, some delays must added. Or it will be quite dead. You will find the timing details in the LCD datasheet. Feel free to ask about this matter here
Now will be a good time to crank up the software simulator in MPLAB. Take a good look on my posting here.