serial LCD 1602 Backpack using PIC16F690 for Hitach HD44780

[jackberg1]

edited BaudR var word : baudr = 3313 and TRISA = 111110

1st receiving random characters
2nd normal

what could be done to avoid the first
thanks.

[richard]

its always better to use the hardware than bit-banged routines and there is nothing better than a ring-buffer to overcome traffic snarls

'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' 
' Name  : 16F690 LCD BACKPACK
' Date  : oct 2025    richard
' Note  : RING BUFFERED
' Notes : 19200 Intrc_OSC 8Mhz
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
#CONFIG
cfg = _INTRC_OSC_NOCLKOUT 
cfg&= _WDT_OFF
cfg&= _PWRTE_OFF
cfg&= _MCLRE_OFF
cfg&= _CP_OFF
cfg&= _CPD_OFF
cfg&= _BOD_OFF
cfg&= _IESO_OFF
cfg&= _FCMEN_OFF
  __CONFIG cfg
#ENDCONFIG
    DEFINE OSC 8  
    DEFINE INTHAND myint 
    ANSEL = 0           ' Set all pins digital
    ANSELH = 0          ' Set all pins digital
    OPTION_REG.7 = 0    ' PORTA/PORTB pull-ups are enabled by individual port latch values
    
    CLEAR
    DEFINE LCD_BITS 8     'defines the number of data interface lines (4 or 8) 
    DEFINE LCD_DREG PORTC    'defines the port where data lines are connected to
    DEFINE LCD_RSREG PORTB    'defines the port where RS line is connected to
    DEFINE LCD_RSBIT 6     'defines the pin where RS line is connected to 
    DEFINE LCD_EREG PORTB     'defines the port where E line is connected to 
    DEFINE LCD_EBIT 4     'defines the pin where E line is connected 
    DEFINE LCD_COMMANDUS 1500     'defines the delay after LCDOUT statement 
    DEFINE LCD_DATAUS 50         'delay in micro seconds


    RCSTA = $90   ' Enable serial port & continuous receive
    TXSTA = $20   ' Enable transmit, BRGH = 0
    SPBRG = 25    ' 19200 Baud @ 8MHz, 0.16%
    SPBRGH = 0
    BAUDCTL.3 = 1 ' Enable 16 bit baudrate generator


    wsave VAR BYTE $70 SYSTEM ;wsave in access RAM
    ssave VAR BYTE BANK0 SYSTEM
    psave VAR BYTE BANK0 SYSTEM
    index_in         VAR BYTE bank0         ' Pointer - next empty location in buffer
    index_out        VAR BYTE bank0         ' Pointer - location of oldest character in buffer
    errflag          VAR BYTE bank0         ' Error flag
    UartFlag         VAR errflag.0
    BufferFlag       VAR errflag.1
    buffer_size      CON  32                               ' Sets the size of the ring buffer  
    buffer           VAR  BYTE[buffer_size]     ' Array variable for holding received characters 
    bufchar          VAR  BYTE          ' Stores the character retrieved from the buffer
    Bl               var byte 
 
    


GOTO overint ' Jump over the interrupt handler 
ASM
myint
   if CODE_SIZE <= 2 ; If less than 2K code space
        ; Save the state of critical registers (PIC12/PIC16)
       movwf wsave ; Save W
       swapf STATUS,W ; Swap STATUS to W (swap avoids changing STATUS)
       clrf STATUS ; Clear STATUS
       movwf ssave ; Save swapped STATUS
       movf PCLATH,W ; Move PCLATH to W
       movwf psave ; Save PCLATH
   endif
; Check for hardware overrun error
   btfsc   RCSTA,OERR   ; Check for usart overrun
   goto    usart_err    ; jump to assembly error routine
; Test for buffer overrun               
   incf   _index_in,W   ; Increment index_in to W
   subwf  _index_out,W  ; Subtract indexes to test for buffer overrun
   btfsc  STATUS,Z      ; check for zero (index_in = index_out)
   goto  buffer_err    ; jump to error routine if zero
; Increment the index_in pointer and reset it if it's outside the ring buffer
   incf   _index_in,F   ; Increment index_in to index_in
   movf   _index_in,W   ; Move new index_in to W
   sublw  _buffer_size-1; Subtract index_in from buffer_size-1
   btfss  STATUS, C     ; If index_in => buffer_size
   clrf   _index_in     ; Clear index_in
; Set FSR with the location of the next empty location in buffer
   movlw    _buffer  ;Store the High byte of buffer to FSR 
   movwf   FSR
   addwf   _index_in,W  ; Add index_in to point to next empty slot
   movwf   FSR        ; Store Low byte of pointer in FSR
; Read and store the character from the USART           
   movf   RCREG,W       ; Read the received character
   movwf  INDF          ; Put the received character in FSR  location
   BTFSC  PIR1,RCIF     ;ANY MORE ?
   goto    myint
finished 
; Restore the state of critical registers (PIC12/PIC16)
   movf psave,W ; restore PCLATH
   movwf PCLATH
   swapf ssave,W ; restore STATUS
   movwf STATUS
   swapf wsave,F ; restore W (swap avoids changing STATUS)
   swapf wsave,W
   retfie ; Return from interrupt 
; Error routines        
buffer_err              ; Jump here on buffer error
   bsf   _errflag,1     ; Set the buffer flag
usart_err               ; Jump here on USART error
   bsf   _errflag,0     ; Set the USART flag
   movf  RCREG, W       ; Trash the received character
   goto finished       ; Restore state and return to program
ENDASM
overint: 
    TRISC = 0
    TRISB = % 10101111
    TRISA = % 11111110 
    OSCCON = $70
    PAUSE 500
    hserout ["ready @19200"]
    LCDOUT $FE,1
    LCDOUT "ready @19200"
    PAUSE 500
@  bsf   LCD_RSREG ,LCD_RSBIT
    INTCON = $C0
    PIE1.5 = 1
GOSUB ERROR
main:
   IF errflag Then GOSUB error ' Goto error routine if needed
   IF index_in = index_out Then main ' loop if nothing in buffer     
   GoSub getbuf         ' Get a character from buffer   
'   hserout [bufchar]        ' Send the character to terminal
   if bl then
        if bufchar = 0 then 
             porta.0 = 0  ' Back Light OFF
        endif
        if bufchar = 8 then 
             porta.0 = 1 ' Back Light ON
        endif
        bl = 0
        goto main
   endif
   if bufchar = 255 then 
         bl = 1
         goto main
   endif
   if bufchar = 254 then
@  bcf   LCD_RSREG ,LCD_RSBIT
         goto main 
   endif 
@  MOVE?BB _bufchar,R3
@  L?CALL lcdsend
@  bsf   LCD_RSREG ,LCD_RSBIT
goto main             ' loop back to top
    


error:                          ' Display error message
   INTCON = 0                   ' Disable interrupts while in the error routine
   IF errflag.1 Then            ' Determine the error
      hserout ["B!",13]' Display buffer error on line-2
   Else
      hserout ["U!",13]  ' Display usart error on line_2
   EndIF
   PIR1.5=0      
   errflag = 0          ' Reset the error flag    ;clear any rcsta error
   RCSTA.4=0           'CREN = 0 Disable continuous receive to clear hardware error
   RCSTA.4=1           'CREN = 1 Enable continuous receive
   INTCON = %11000000   ' Enable interrupts
   RETURN         ' repeat


    
getbuf:  ' Move the next character in buffer to bufchar
   index_out = index_out + 1     ' Increment index_out pointer (0 to 31)
   IF index_out => buffer_size Then index_out = 0 ' Reset pointer if outside buffer
   bufchar = buffer[index_out]  ' Read buffer location(index_out)
   Return