Mark

Apart from config fuses which your programmer may let you change anyway, the
obvious problems are that on reset the 877 sets port A to analogue inputs
and needs setting to digital input/output (see data sheet for details of the
ADCONF registers), the RAM is at different addresses but I notice you've
sorted that problem.

Multi-processor projects can be quite easy, just use plenty of #ifdef
statements to set up variables:

#ifdef __P16F84
 F84 stuff here
#endif

#ifdef __P16F877
 F877 stuff here
#endif

etc.


Robin Abbott - robin.abbott@dial.pipex.com

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----- Original Message -----
From: Mark Crankshaw <mic1000@HERMES.CAM.AC.UK>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: 07 October 1999 11:34
Subject: 'F84 to 'F877 problems


> I'm still quite new to PICs (and have just returned to the list after a
> break) but have used 'F84s successfully for a couple of projects. Now that
> I can obtain 'F877s I am trying to convert my projects to use the 'F877 so
> that I can then expand the projects.
>
> However I'm having problems. I started by simply changing register
> addresses to suit the 'F877 but that didn't work. To cut a long story
> short I'm now back to trying to get LEDs to flash! I have a simple circuit
> on stripboard with an 'F877, voltage reg.,0.1 uF cap. across the supply, 4
> MHz crystal with 2 15 pF caps., MCLR tied directly to 5V and 8 LEDs with
> resistors on PORTB. The following program works, well kind of - the
> LEDs come on one at a time and then go off rather one running up and
> down the line, but at least it does something (WDT enabled of course):
>
> ;-------------------------------------------------------------
>         LIST P=16F877
> ;
> PORTB   EQU     6
> TRISB   EQU     86H
> OPTREG  EQU     81H
> STATUS  EQU     3
> CARRY   EQU     0
> RP0     EQU     5
> MSB     EQU     7              ;BIT POSITION OF LEFTMOST LED
> ;
>         CLRF    PORTB           ;ALL LEDS OFF
>         BSF     STATUS,RP0      ;SELECT REGISTER BANK 1
>         CLRF    TRISB^80H       ;SET PORTB TO ALL OUTPUTS
>         MOVLW   0AH
>         MOVWF   OPTREG^80H      ;ASSIGN PRESCALER (1:4) TO WDT
>         BCF     STATUS,RP0      ;SELECT REGISTER BANK 0
>         INCF    PORTB,F         ;TURN ON RIGHTMOST LED
>         BCF     STATUS,CARRY    ;CLEAR CARRY
> LEFT    SLEEP                   ;WAIT FOR WDT TIMEOUT
>         RLF     PORTB,F         ;TURN ON LED TO LEFT
>         BTFSS   PORTB,MSB       ;REACHED LEFTMOST?
>         GOTO    LEFT            ;LOOP IF NOT
> RIGHT   SLEEP                   ;WAIT FOR WDT TIMEOUT
>         RRF     PORTB,F         ;TURN ON LED TO RIGHT
>         BTFSS   PORTB,0         ;REACHED RIGHTMOST?
>         GOTO    RIGHT           ;LOOP IF NOT
>         GOTO    LEFT            ;START NEW CYCLE
>         END
> ;-------------------------------------------------------------
>
> However the following doesn't (WDT off):
>
> ;-------------------------------------------------------------
>         LIST P=16F877
> ;
> PORTB   EQU     6
> TRISB   EQU     86H
> OPTREG  EQU     81H
> STATUS  EQU     3
> CARRY   EQU     0
> RP0     EQU     5
> MSB     EQU     7              ;BIT POSITION OF LEFTMOST LED
> LOOP1   EQU     20H
> LOOP2   EQU     21H
> ;
>         CLRF    PORTB           ;ALL LEDS OFF
>         BSF     STATUS,RP0      ;SELECT REGISTER BANK 1
>         CLRF    TRISB           ;SET PORTB TO ALL OUTPUTS
>         MOVLW   0AH
>         MOVWF   OPTREG^80H      ;ASSIGN PRESCALER (1:4) TO WDT
>         BCF     STATUS,RP0      ;SELECT REGISTER BANK 0
>         INCF    PORTB,F         ;TURN ON RIGHTMOST LED
>         BCF     STATUS,CARRY    ;CLEAR CARRY
>
> START   MOVLW   0FFH
>         MOVWF   LOOP1
> L1      MOVLW   0FFH
>         MOVWF   LOOP2
> L2      DECFSZ  LOOP2
>         GOTO    L2
>         DECFSZ  LOOP1
>         GOTO    L1
>         INCF    PORTB,F
>         GOTO    START
>         END
> ;-------------------------------------------------------------
>
> I also tried the above with the WDT on and with a CLRWDT in L2 but that
> didn't help. I don't think you can get much simpler than this yet I can't
> get it to work. Incidentally I've tried two different 'F877s, three
> crystals and also with and without a 1k resistor between CLKOUT and the
> oscillator in case that was the problem.
>
> So can anyone help? I'm sure I must be overlooking something very simple
> but I don't know what.
>
> Thanks,
>
> Mark.