Philip
     
     What is the circuitry connected to port B?
     
     I assume it's two banks of 8 DIP switches, each driven by a switchable 
     supply - If so, have you got a diode in series with each DIP switch, 
     so that powering one bank, doesn't power the other bank by feeding 
     back thou' the other DIP switch.
     
                Steve Lawther 


______________________________ Reply Separator _________________________________
Subject:      Port B Problems
Author:  PC:philip@PHILMART.DEMON.CO.UK at INTERNET-HUSKY
Date:    19/12/97 08:22


I sent this message earlier today from my machine at work and think I 
used the wrong address, dammm machine:-(
     
     
Hi all,
     
Hope this gets through only I'm not using my normal PC base!
     
Having some problems, code I think with a 16C64 and port B.
     
The code snippets below show 'A the initialisation of the ports and 'B 
the code to talk to the port. The idea is that at the start of the prog, 
data from some BCD switches is read into the pic.
     
The problem is that whilst the pulses and port A are working correctly, 
port B aint. It seams to be sitting high, 5v. 10k's pulling it down only 
take the voltage down to about 1.4v, thus any lines high from the BCD 
switches are not distinguishable from the others and the value read from 
the port is always FF. If I completely ground the lines from the port 
this has no effect other than the pic seems to ignore any value from this 
port. When the lines are grounded, a current of about 160uA is flowing 
through them.
     
What have I forgotten or got wrong?
     
Code A
init    clrf    porta           ; clear port
        clrf    portb           ; clear port 
        clrf    portc           ; clear port 
        clrf    portd           ; clear port 
        clrf    porte           ; clear port
        bsf     pa1             ; selected page 1
        movlw   b'00000101'     ; set initialisation of rtcc
        movwf   optreg          ; load option reg with prescale of 64 
        movlw   b'1111'         ; set port a i/o
        movwf   trisa           ; set the ddr 
        movlw   b'11111111'     ; set port b i/o 
        movwf   trisb           ; set the ddr 
        movlw   b'00000000'     ; set port c i/o 
        movwf   trisc           ; set the ddr 
        movlw   b'00000000'     ; set port d i/o 
        movwf   trisd           ; set the ddr 
        clrf    trise           ; set port e i/o
     
        bcf     pa1             ; selected page 0
     
        call    clearreg        ; subroutine to clear all registers 
        call    bcdget          ; subroutine to get bcd switch settings 
        movlw   .100            ; put initial value in rtcc
        movwf   rtcc
        movlw   b'10100000'     ; enable global & rtcc interrupts 
        movwf   intcon
     
Code B
     
bcdget  clrf    porte           ; start with a clear port
        bsf     switch12        ; turn on switch 1+2 power
        call    delay1          ; allow time for port voltage to settle 
        movfw   portb           ; get switch settings
        movwf   r0              ; and put into reg 
        bcf     switch12        ; turn off switch 1 
        nop
        bsf     switch34        ; turn on switch 3+4 power 
        call    delay1
        movfw   portb
        movwf   r1
        bcf     switch34
        nop                     ; end sub
        return
--
Philip Martin   email philip@philmart.demon.co.uk
     
Royal Quays, North Shields.
     
--
Philip Martin   email philip@philmart.demon.co.uk 
Royal Quays, North Shields