The portion of code related to the LCD locate is as follows (you'll see all
this better in Courier or  any monospaced font)

        movlw   H'40'
        call    locate     ; "Locate 40"

Then, in the subroutines section, is the 'locate' subroutine: (Sorry for the
spanish comments. If you need, I'll try to translate them...). The full
program code is now 'slightly' long, so I put here only the code related to
the LCD. What most bother me is that this code works OK with all addresses
but '00' and '40'...

As you can see, the 'locate' subroutine only sets the 7 bit of W, where the
DDRAM address is, and then goes on the subroutine 'princmd'. This one clears
the pin 'lcd_rs', to tell the LCD that a command is to be performed, and
jumps to the 'envlcd' routine. 'envlcd' sends both the high and the low
nibble of W (temporary saved in 'aux') to 'lcdbus', the port in wich the 4
LCD data pins are connected. This port is used to other things as well, so I
need to preserve the low nibble of the port.

The definitions used in this code portion are:

; Definiciones para el LCD
#define lcd_e   PORTE,2    ; "Enable" del LCD
#define lcd_rs  PORTE,1    ; "Register Select" del LCD
#define lcdbus  PORTD      ; El bus del LCD (entrada/salida)
#define lcdmasc B'11110000'; M‡scara para preservar los bits
                           ; de lcdbus que no son del LCD

The subroutines:

; Posiciona el cursor del LCD en la posici—n que marca W
; Las direcciones para el locate en un LCD 16x2 son:
;   +-------------------------------------------------+
;   | 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F |
;   | 40 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F |
;   +-------------------------------------------------+
locate  iorlw   B'10000000'; Asegura "Set DDRAM address"
                           ; y env’a el comando (princmd)
; Env’a byte en W al LCD (Bus de 4 bits)
princmd bcf     lcd_rs     ; El byte es un comando
        goto    envlcd
princhr bsf     lcd_rs     ; El byte es un car‡cter
envlcd  movwf   aux        ; Salva el car‡cter

        movlw   lcdmasc ^ B'11111111'; Salva los 4 bits
        andwf   lcdbus,W   ; del puerto del LCD que no per-
        movwf   aux1       ; tenecen al dato a transmitir

        movf    aux,W      ; Une el primer nibble a enviar
        andlw   lcdmasc    ; con la parte del puerto preser-
        iorwf   aux1,W     ; vada...
        movwf   lcdbus
        bsf     lcd_e      ; y lo env’a.
        nop
        bcf     lcd_e

        swapf   aux,W      ; Lo mismo con el segundo nibble
        andlw   lcdmasc
        iorwf   aux1,W
        movwf   lcdbus
        bsf     lcd_e      ; y lo env’a.
        nop
        bcf     lcd_e      ; ...y espera 100us

; Bucle de espera de 100us=0.1ms. S—lo afecta al reg. W
buc100  movlw   d'256'-d'100'*fosc/4/4
                ;         |     |  | +-> instrucciones/bucle
                ;         |     |  +---> cicl_reloj/instruc.
                ;         |     +------> Frec. cristal (MHz)
                ;         +------------> 100us
        addlw   D'1'
        btfss   STATUS,Z
        goto    $-2
        return



-----Mensaje original-----
De: McMeikan, Andrew <andrew.mcmeikan@MITSWA.COM.AU>
Para: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Fecha: lunes, 30 de agosto de 1999 11:50
Asunto: Re: LCD DDRAM address problems


>Hi Alvaro,
>        I assume that you are sending this with bit 7 high, most data
sheets
>call the addresses 80-8F and C0-CF to avoid that ambiguity, other wise you
>should have no problem, what about a snippet of the source code? pin
>assignments, do you have a pin open-collector?
>
>        cya,    Andrew...
>
>> -----Original Message-----
>> From: Alvaro Deibe Diaz [SMTP:adeibe@CDF.UDC.ES]
>> Sent: Monday, August 30, 1999 5:13 PM
>> To:   PICLIST@MITVMA.MIT.EDU
>> Subject:      LCD DDRAM address problems
>>
>> Hi piclisters,
>>
>> I have problems trying to make a "locate" in an Optrex LCD. The LCD has
>> the
>> typicall Hitachi 77480 in it. It is 16char x 2lines, so I suppose the
>> DDRAM
>> address for the 32 possible locations (without shift) are:
>>
>> 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
>> 40 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F
>>
>> The "Set DDRAM Address" command seems to work OK for the last 15 char in
>> each line, but fails with addresses '00' and '40', apparently "hanging"
>> the
>> 44780. ÀAny ideas?
>>
>> Note: the interface is 4-bits long, and the uC a 16C65
>>
>> Thanks.
>