serial LCD 1602 Backpack using PIC16F690 for Hitach HD44780

[richard]

My code honours the timing as specified by the lcd defines , timing that most lcd displays need esp the cheapest and oldest examples of them.
If you send data at a rate that exceeds the specified time constraints as defined it will of course fall. The solution is to either pace data transmission or set the defines to the actual speed the lcd can tolerate . The intent of my code is to match data rate to the real speed that the lcd can manage

[jackberg1]

set pace to 1 , and it's working
sEROUT2 lcd,baudR,pace,[254,128,"ABCDEFGHIJKLMNOP"]

thanks.

[Ioannis]

I only tested at 19200 and the Backlight works OK.

But text, could not send up to this moment.

WIll try different Baud Rate. Though I test on a PIC16F1827 at 32MHz.

Ioannis

[jackberg1]

when testing baud rate, usualy I start at 300 and up

when it stopped working then I set pace = 1

and re-start from the last baud rate tested.

16F690 Xtal 20Mhz

set pace to 1
sEROUT2 lcd,baudR,pace,[254,128,"ABCDEFGHIJKLMNOP"]


from my code here's the tested baud rate .
and when booting the PIC's at different baud rate the sender 12F683 and receiver 16F690 the LCD screen light up right away and start displaying text, and back light on/off
there's no lag for the first receiving if I remember correctly the pace for the sender is set = 0.





Also I add baud rate selection jumpers on the Backpack''







' Jumpers
'
J3 300 600 1200 2400 4800 9600 14400 19200 28800 38400
' 1--2 RB7 On On On On On On
' 3--4 RA2 On On On On
' 5--6 RA1 On On On On
' 7--8 RA3 On On On



' Baud Rate SW Selection (PCB J3)
If PORTA = 001110 And PORTB.7 = 1 Then BaudR = 3313 ' 300
If PORTA = 001110 And PORTB.7 = 0 Then BaudR = 1646 ' 600
If PORTA = 001010 And PORTB.7 = 1 Then BaudR = 813 ' 1200
If PORTA = 001100 And PORTB.7 = 1 Then BaudR = 396 ' 2400
If PORTA = 000110 And PORTB.7 = 1 Then BaudR = 188 ' 4800
If PORTA = 001010 And PORTB.7 = 0 Then BaudR = 84 ' 9600
If PORTA = 001100 And PORTB.7 = 0 Then BaudR = 49 ' 14400
If PORTA = 000110 And PORTB.7 = 0 Then BaudR = 32 ' 19200
If PORTA = 001000 And PORTB.7 = 0 Then BaudR = 15 ' 28800
If PORTA = 000000 And PORTB.7 = 0 Then BaudR = 6 ' 38400

[jackberg1]

from my last edit,

' Jumpers
' J3 300 600 1200 2400 4800 9600 14400 19200 28800 38400
' 1--2 RB7 On On On On On On
' 3--4 RA2 On On On On
' 5--6 RA1 On On On On
' 7--8 RA3 On On On

I think courier new does not take spaces !
better use screen cap

[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

[jackberg1]

ASM , very impressif code,

thanks.

[jackberg1]

here's the revised baud rate test chart