Hello,
I'm having problems with the interrupt on PORT B feature of the 16C84.
I've read the microchip Ap Note on using the 'port b change interrupt'
but it doesn't help much.
I have a rotary encoder from a motor connected to bits 6 and 7 of PORTB.
The output from the rotary encoder is a 2 bit gray code, and I would like
the pic to enter the Interrupt service routine whenever the pattern
changes.
I then need the pic to read PORTB to store the values of bit 6 and 7 in a
register. The output from the rotary encoder just changes logic level, it
does not provide a pulse output. I presume that microchip refers to this
as a 'wide pulse' in there Ap note.
        From what I can make out the PIC isn't reading PORTB correctly if
at all. Does anyone have any idea where I'm going wrong ?
I think that it enters the ISR correctly. but wont get the value on
PORTB. Why does the Ap note include MOVF PORTB,1 as this doesn't seem to
change any of the special function registers in the simulator. What does
this instruction do, and do I have it in the correct place in my code ?

I have managed to simulate the rest of the programme successfully in the
MPLAB simulator, using the clocked stimulus dialogue to get it into the
Interrupt service routine. When I use the modify window to change the
contents of PORTB it only allows me to write to the output bits. Is there
some simple way of getting around this so that I can simulate the input
from the rotary encoder ?


Thanks in advance, any help would be greatly appreciated.
Hamish

TITLE "MOTOR CONTROL"     ; Hamish Dublon 1998 FILE intpc.ASM
; provide basic directional control
        PROCESSOR PIC16C84
        LIST    P=PIC16C84
        INCLUDE P16C84.INC
        ORG 00
#define bank0 BCF STATUS,RP0
#define bank1 BSF STATUS,RP0
        GOTO SETUP

;----------------------------------HANDLE INTERUPT----------
        ORG 04H
INTERUPT
        MOVWF W_SAVE
        SWAPF STATUS,W
        bank0                   ; change to bank 0
        MOVWF S_SAVE

LOOPINT BCF INTCON,GIE          ;disable global interupt
        BTFSC INTCON,GIE        ;is GIE flag disabled, if not do again
        GOTO LOOPINT

        BTFSS INTCON,RBIF       ;check if it is RB[0] or RB[7..4]
        GOTO OTHER_INT          ;RB[0] interupt
        MOVF PORTB,1            ;read port b to itself to end
                                ;the mismatch condition
        BCF INTCON,RBIF ;clear the port b interupt flag
        BCF PORTA,DONE          ;set led
        BSF PORTA,GOT_INT               ;set led
;interupt code for a port B 7..4 change goes here
        MOVF PORTB,W            ;copy portb to w                <---
                                ; **** doesnt seem to work
        ANDLW B'11000000'       ;Mask to select bits 6 and 7

;----------All code from here on simulated corectly-------------
; lots of code here to determine the motor position
;---------------------------------------------------
        GOTO ENDINT


OTHER_INT                       ;RB[0] interupt
;interupt code for RB[0] change goes here
        MOVF PORTB,1            ;read port b to itself to end the mismatch condi
tion
        BCF INTCON,INTF         ;clear the RB[0] interupt flag

        CLRF PORTB              ;Clear port B
        CLRF GLOBAL_POS

ENDINT  SWAPF   S_SAVE,W        ;restore w register
        MOVWF   STATUS          ;restore status register
        SWAPF   W_SAVE,W
        BSF INTCON,INTE         ;ENABLE INTF interupt ***************
        BSF INTCON,RBIE         ;ENABLE interupt on port b change
        BCF INTCON,T0IF         ;FLAG 0, timer did not overflow
        BCF INTCON,INTF         ;FLAG 0, RB0 interupt did not occur
        BCF INTCON,RBIF         ;FLAG 0, portb 7..4 have not changed
        BSF INTCON,GIE          ;1 Enable global interupts
        RETFIE                  ;return from interupt

SETUP

        MOVLW B'10000'                  ; SET BIT 4 INPUT, 0,1,2,3 OUTPUTS
        TRIS PORTA                      ; SET DDR
        CLRF PORTA                      ; CLEAR THE PORT
        MOVLW B'11110001' ; SET PORT B 7,6,5,4,0 inputs,  3,2,1 outputs
        TRIS PORTB                      ; SET DDR
        CLRF PORTB