Andreas,

Is it possible the circuitry you are driving with pin RB3 is holding it high?

Try modifying your program to execute CLRF PORTB in a continuos loop. If it
still stays high, the problem is the external circuit requires more PIC sink
current than the PIC has capability for.

Steve Buckser




Andreas Magnusson <andreas.m@TELIA.COM> on 06/07/99 12:23:02 PM

Please respond to pic microcontroller discussion list <PICLIST@MITVMA.MIT.EDU>

To:   PICLIST@MITVMA.MIT.EDU
cc:    (bcc: Steve Buckser/Marketing/San Leandro/Prescolite)
Subject:  Big bad portb problem...




Hello!

I have a problem.... I have programmed a "test program" for a robot I have
built (PIC16F84 used). The program controlls a stepmotorcard. Everything
seems to work exept one thing RB3 pin is allways high... The pin should
pulse like the other ones. I have checed the circuitboard and also tested
with two different MCU:s. I programmed a small program to only clear portb
it worked. I cant really understund why the pin allways is high....


/Andreas Magnusson


LIST P=16F84
 INCLUDE "P16C84.INC"
;*************************
RAM ORG 0x0C
CNT RES 1
CN1 RES 1
CN2 RES 1
TEMP RES 1
M3 RES 1

ORG 0
 GOTO START
ORG 0X30
;*************************
START
 BSF STATUS,RP0
 CLRF TRISA
 CLRF TRISB

 BCF STATUS,RP0
 CLRF PORTA
 CLRF PORTB


M3A
         CLRF PORTA
         BSF PORTB,6
         BCF PORTB,7
         CALL KORTM3                    ;porta works as a adressbuss and
select Motorcard 3
         CLRF M3
M3TABLE
         MOVF M3,W
         CALL FTABLE
         MOVWF PORTB
         NOP
         BCF PORTB,6                        ;clocking in the value from
ftable into a data latch on the stepmotorcard
         NOP
         BSF PORTB,6
         MOVLW .130
         CALL DELAY
         INCF M3
         MOVLW .7
         XORWF M3
         BTFSC STATUS,Z
         CLRF M3
         GOTO M3TABLE

;*****************************
FTABLE ADDWF PCL
 RETLW B'01001111'
 RETLW B'01001001'
 RETLW B'01110001'
 RETLW B'01000001'
 RETLW B'01000110'
 RETLW B'01000000'
 RETLW B'01111000'
 RETLW B'01001100'

;*****************************
KORTM3 BSF STATUS,RP0
 CLRF TRISA
 CLRF TRISB

 BCF STATUS,RP0
 MOVLW 06h
 MOVWF PORTA
 RETURN

;*****************************
DELAY MOVWF   CN2
LOOP    MOVWF   CN1
AGAIN   NOP
 NOP
 NOP
 NOP
 DECFSZ  CN1,F
 GOTO    AGAIN
 DECFSZ  CN2,F
 GOTO    LOOP
 RETURN
;********************************************************
end