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12F675 GPIO3/MCLR - How do you get it to work as an input?

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Y

Yobortsa

Member
This one's baffling me.

Why can't I use GPIO3 as an input? The code below works using GPIO5 as the Serial input line.

It also works if I change to GPIO4:

Code: 
SER_IN		Equ	0x04

But as soon as I try GPIO3, I get continuous duplicate characters coming in - I think it's reading lows continously. I did add some code at one point to send a 1 or 0 via RS232 to tell me the level of GPIO3 and it worked fine as I alternated between Vdd and Vss. So why isn't it working from the MAX232? Why does it work on GPIO4 and 5 but not 3?

Code: 
	list p=12F675, b=8, c= 102, n=71, t=on, st=off, f=inhx32

	#include	<p12f675.inc>
	errorlevel	-302

     __CONFIG (_INTRC_OSC_NOCLKOUT & _WDT_OFF &_BODEN_OFF &_CP_OFF &_CPD_OFF & _MCLRE_OFF)

;***** FLAGS
#define 	IF_SHORT 	flags, 0
#define 	FIRST_HALF 	flags, 1
#define 	HEADER 		flags, 2
#define 	VALID 		flags, 7

;***** VARIABLE DEFINITIONS

	cblock 	0x20 			;start of general purpose registers

				Xmit_Byte        	;holds byte to xmit
            	Rcv_Byte        	;holds received byte 
            	Bit_Cntr        	;bit counter for RS232
            	Delay_Count        	;delay loop counter

	endc

SER_PORT	Equ	GPIO
SER_TRIS	Equ	TRISIO
SER_IN		Equ	0x05
SER_OUT		Equ	0x04

	org	0x0000

RESET	bcf		STATUS,RP0		; Bank 0
;		clrf	STATUS			;
		clrf	GPIO			; Init GPIO
		movlw	b'00000111'		;
		movwf	CMCON			; comparator off, digital I/O

		bsf     STATUS,RP0      ; bank 1
		clrf	ANSEL			; Digital I/O

		movlw   b'00101000'     ; 
        movwf   TRISIO          ; Set GPIOs (1=input/0=output)

        call    h'3FF'          ; get factory calibration value
        movwf   OSCCAL          ; set OSCCAL calibration value

        bcf     STATUS,RP0      ; bank 0                          |B0

		call	SER_INIT		; initialise serial port

; Startup beeps...

		bsf		GPIO, 0
		call delay100
		bcf		GPIO, 0
		call delay100
		bsf		GPIO, 0
		call delay100
		bcf		GPIO, 0

loop
		call	Rcv_RS232

;		movf	Rcv_Byte

		movlw	'0'
		xorwf	Rcv_Byte,0
		btfsc	STATUS, Z
		bcf		GPIO, 0

		movlw	'1'
		xorwf	Rcv_Byte,0
		btfsc	STATUS, Z
		bsf		GPIO, 0

		movlw	'2'
		xorwf	Rcv_Byte,0
		btfsc	STATUS, Z
		bcf		GPIO, 1

		movlw	'3'
		xorwf	Rcv_Byte,0
		btfsc	STATUS, Z
		bsf		GPIO, 1

		movlw	'4'
		xorwf	Rcv_Byte,0
		btfsc	STATUS, Z
		bcf		GPIO, 2

		movlw	'5'
		xorwf	Rcv_Byte,0
		btfsc	STATUS, Z
		bsf		GPIO, 2

		movlw	'6'
		xorwf	Rcv_Byte,0
		btfsc	STATUS, Z
		bcf		GPIO, 4

		movlw	'7'
		xorwf	Rcv_Byte,0
		btfsc	STATUS, Z
		bsf		GPIO, 4

		movlw	'a'
		xorwf	Rcv_Byte,0
		btfsc	STATUS, Z
		goto beep1

		movlw	'b'
		xorwf	Rcv_Byte,0
		btfsc	STATUS, Z
		goto beep2

		movlw	'c'
		xorwf	Rcv_Byte,0
		btfsc	STATUS, Z
		goto beep3

		movlw	'd'
		xorwf	Rcv_Byte,0
		btfsc	STATUS, Z
		goto beep4

		movlw	'e'
		xorwf	Rcv_Byte,0
		btfsc	STATUS, Z
		goto beep5

		movlw	'f'
		xorwf	Rcv_Byte,0
		btfsc	STATUS, Z
		goto beep6

		movlw	'g'
		xorwf	Rcv_Byte,0
		btfsc	STATUS, Z
		goto beep7

		movlw	'h'
		xorwf	Rcv_Byte,0
		btfsc	STATUS, Z
		goto beep8

		movlw	'i'
		xorwf	Rcv_Byte,0
		btfsc	STATUS, Z
		goto beep9

		goto loop

beep1	bsf		GPIO, 0
		call delay100
		bcf		GPIO, 0
		goto	loop

beep2	bsf		GPIO, 0
		call delay250
		bcf		GPIO, 0
		goto	loop

beep3	bsf		GPIO, 0
		call delay250
		call delay250
		bcf		GPIO, 0
		goto	loop

beep4	bsf		GPIO, 0
		call delay250
		call delay250
		call delay250
		bcf		GPIO, 0
		goto	loop

beep5	bsf		GPIO, 0
		call delay250
		call delay250
		call delay250
		call delay250
		bcf		GPIO, 0
		goto	loop

beep6	bsf		GPIO, 0
		call delay100
		bcf		GPIO, 0
		call delay100
		bsf		GPIO, 0
		call delay100
		bcf		GPIO, 0
		goto	loop

beep7	bsf		GPIO, 0
		call delay100
		bcf		GPIO, 0
		call delay100
		bsf		GPIO, 0
		call delay250
		call delay250
		bcf		GPIO, 0
		goto	loop

beep8	bsf		GPIO, 0
		call delay250
		call delay250
		bcf		GPIO, 0
		call delay100
		bsf		GPIO, 0
		call delay100
		bcf		GPIO, 0
		goto	loop

beep9	bsf		GPIO, 0
		call delay250
		call delay250
		bcf		GPIO, 0
		call delay100
		bsf		GPIO, 0
		call delay250
		call delay250
		bcf		GPIO, 0
		goto	loop

;-----------------------------------------------
;Serial routines

SER_INIT
            BSF     STATUS, RP0           ;select bank 1
;            BCF     SER_TRIS, SER_OUT     ;set B6 as an output
            BSF     SER_TRIS, SER_IN      ;set B7 as an input
            BCF     STATUS, RP0           ;select bank 0
;            BSF     SER_PORT, SER_OUT     ;set SER_OUT high
            RETURN

Rcv_RS232   BTFSC   SER_PORT, SER_IN      ;wait for start bit
            GOTO    Rcv_RS232
            CALL    Start_Delay	          ;do half bit time delay
            BTFSC   SER_PORT, SER_IN      ;check still in start bit
            GOTO    Rcv_RS232
            MOVLW   0x08                  ;set up to read 8 bits
            MOVWF   Bit_Cntr
            CLRF    Rcv_Byte
Next_RcvBit CALL    Bit_Delay
            BTFSS   SER_PORT, SER_IN
            BCF     STATUS    , C
            BTFSC   SER_PORT, SER_IN
            BSF     STATUS    , C
            RRF     Rcv_Byte  , f
            DECFSZ  Bit_Cntr  , f         ;test if all done
            GOTO    Next_RcvBit
            CALL    Bit_Delay
            MOVF    Rcv_Byte, W
            RETURN

Start_Delay MOVLW   0x0C
            MOVWF   Delay_Count
Start_Wait  NOP
            DECFSZ  Delay_Count , f
            GOTO    Start_Wait
            RETURN

;Bit_Delay   MOVLW   0x18   ; Original setting in code - wasn't working reliably at 9600baud
Bit_Delay   MOVLW   0x17
            MOVWF   Delay_Count
Bit_Wait    NOP
            DECFSZ  Delay_Count , f
            GOTO    Bit_Wait
            RETURN

;End of serial routines
;-----------------------------------------------

; Delay = 0.25 seconds
; Clock frequency = 4 MHz

; Actual delay = 0.25 seconds = 250000 cycles
; Error = 0 %

	cblock
	d1
	d2
	endc

			;249998 cycles
delay250
	movlw	0x4F
	movwf	d1
	movlw	0xC4
	movwf	d2
Delay_0
	decfsz	d1, f
	goto	$+2
	decfsz	d2, f
	goto	Delay_0

			;2 cycles
	goto	$+1

; Generated by http://www.piclist.com/cgi-bin/delay.exe (December 7, 2005 version)
; Sat Dec 31 06:04:07 2011 GMT

; See also various delay routines at http://www.piclist.com/techref/microchip/delays.htm 
	return

; Delay = 0.1 seconds
; Clock frequency = 4 MHz

; Actual delay = 0.1 seconds = 100000 cycles
; Error = 0 %

;	cblock
;	d1
;	d2
;	endc

			;99998 cycles
delay100
	movlw	0x1F
	movwf	d1
	movlw	0x4F
	movwf	d2
Delay_1
	decfsz	d1, f
	goto	$+2
	decfsz	d2, f
	goto	Delay_1

			;2 cycles
	goto	$+1

; Generated by http://www.piclist.com/cgi-bin/delay.exe (December 7, 2005 version)
; Sat Dec 31 06:07:36 2011 GMT

; See also various delay routines at http://www.piclist.com/techref/microchip/delays.htm 
	return

		end

What's different about GPIO3 as an input compared to GPIO4 and GPIO5? Is there some configuration I'm missing? I've disabled MCLR (as far as I know).

Thanks,

David
 
The only difference is that GPIO3 is open collector..
Click to expand...

Not true.
GPIO 3 is input only. It is a normal input pin. You will have no problems with this pin as an input.
 
Thanks for your suggestions Ian and Colin.

I did try a pullup and large value resisters to ground to no avail. I've also been over the data sheet and through the P12F675.INC include file but still don't know why it wasn't working. Also tried a new PIC chip incase there was a fault with the other one. I'd still like to know why it wasn't working - I ended up using GPIO5 in this instance, but I would have put an extra LED on the keypad if I could get it working. I don't like wasting pins!

I had similar issues with a PIC16F628A yesterday until I realised there is a config register (_LVP_OFF) to disable low voltage programming on pin RB4 which I was trying to use.

Thanks,

David
 
You are simply not making GPIO,3 and INPUT
Put a sw and 100n and 22k on the input and create a loop that just looks at the input.

Let us know
 
The max should be able to toggle GP3. First off your not posting code that used GP3 it's using GP5 so how is any one to tell if you have it set right when you change
to GP3 In Mplabsim your code is setting the pins right
Code: 
SER_PORT	Equ	GPIO
SER_TRIS	Equ	TRISIO
SER_IN		Equ	0x05
SER_OUT		Equ	0x04

Try this
Code: 
SER_PORT	Equ	GPIO
SER_TRIS	Equ	TRISIO
SER_IN		Equ	0x03
SER_OUT		Equ	0x04

See if you pulled the pinup like pic
 

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