Tim,
To define a custom character on an HD44780 LCD, you send out a
command to build the
character followed by a sequence of characters just like any
other string.  Here are
a bunch of routines that I use:

        movlw   0x40            ; create two custom designed
characters from bitmaps at M5Start
        call    SndLCDCmd       ; set CGRAM address to
character 0
        movlw   LOW (M5Start - M1Start) ; set pointer to start
of string
        call    SndLCDStr

        movlw   0x00            ; output 1st user defined symbol
        call    SndLCDChr

; -------------------------------
; Subroutines
; -------------------------------

SndLCDCmd                       ; send the command in w
        bcf     PortLCD, RS     ; drive RS low (command)
        movwf   LCDTemp
        call    PortNibble
        call    PulseE
        swapf   LCDTemp, W
        call    PortNibble
        call    PulseE
        call    d20ms           ; overkill as 1.64ms is worst-
case spec
        return

SndLCDChr                       ; send the character in w
        bsf     PortLCD, RS     ; drive RS high (character)
        movwf   LCDTemp
        call    PortNibble
        call    PulseE
        swapf   LCDTemp, W
        call    PortNibble
        call    PulseE
        call    d20us
        call    d20us
        return

SndLCDStr                       ; w must contain the offset of
the string to output
        movwf   ChrCnt
SndLoop call    GetLCDChr       ; return with character to
output in w
        xorlw   0x00            ; test if it's zero
        btfsc   STATUS, Z
        return                  ; return if character is 0x00
        call    SndLCDChr       ; output character
        incf    ChrCnt, F       ; pointer for next character
        goto    SndLoop

PulseE  bsf     PortLCD, E      ; take E high
        nop                     ; pause 1us. At least 450ns
required.
        bcf     PortLCD, E      ; take it low
        return
NybbletoASCII                   ; convert a Nybble in "w" to
ASCII
        addlw   0x036           ; add '0' + 6 to Value
        btfsc   STATUS, DC      ; if Digit Carry Set, then 'A' -
 'F'
        addlw   7               ; add Difference Between '9'
and 'A'
        addlw   0-6             ; subtract 6
        btfss   Flags, SLZ      ; return if Suppress Leading
Zero flag is not set
        return
        addlw   0 - "0"
        btfsc   STATUS, Z
        retlw   0x00            ; return 0 if SLZ set and
character is a leading zero
        addlw   "0"
        bcf     Flags, SLZ      ; After a non-zero character,
turn off zero supression
        return

PortNibble
        andlw   0xf0            ;
        iorwf   PortLCD, F      ; Use the lower four bits of
PortLCD
        iorlw   0x0f
        andwf   PortLCD, F
        return


NybbletoASCII                   ; convert a Nybble in "w" to
ASCII
        addlw   0x036           ; add '0' + 6 to Value
        btfsc   STATUS, DC      ; if Digit Carry Set, then 'A' -
 'F'
        addlw   7               ; add Difference Between '9'
and 'A'
        addlw   0-6             ; subtract 6
        btfss   Flags, SLZ      ; return if Suppress Leading
Zero flag is not set
        return
        addlw   0 - "0"
        btfsc   STATUS, Z
        retlw   0x00            ; return 0 if SLZ set and
character is a leading zero
        addlw   "0"
        bcf     Flags, SLZ      ; After a non-zero character,
turn off zero supression
        return

PortNibble
        andlw   0xf0            ;
        iorwf   PortLCD, F      ; Use the lower four bits of
PortLCD
        iorlw   0x0f
        andwf   PortLCD, F
        return

I think I got them all.  If I missed anything, let me know.
These routines also have a
bunch of flags to select zero-supression.  It might be easiest
for you to ignore those.

Andrew


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---- On    , Tim Webb (tim_webb@AGILENT.COM) wrote:

> Has anyone been successful at creating custom characters on
an HD44780
> compatible LCD Display.
>
> I can not make any sense out of my Hitachi Data Sheet.
>
> Does anyone have any sample code, I am using 16F877.
>
> Best Regards,
>
> Tim
>
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