PIC12F683 pin GP3 as output

[louislouis]

Hello folks,
before I tried play with picbasic I worked with PICAXE. I have done few projects with PICAXE 08M2 which is a rebranded PIC12F683 with bootloader.
In PICAXE is one simple cheat which allows to use the pin3 (MCLRE) as output. Pin3 drives an NPN transistor via manipulating weak pullup resistor. In attachment find the schematis which I use wery often. It works fine all the time.
For example here is a simple led blinking code in PICAXE looks like:

#picaxe 08m2
do
pullup $08    ;pullup on GPIO.3 LED ON
pause 500
disable          ;disable pullups LED OFF
pause 500
loop

Now the question is how do they made it? I try similar on PIC12F683 in picbasic but no success.
Try to led blinking code in picbasic like:

;PIC12F683

TRISIO=0
ANSEL=0
OPTION_REG.7=1   ;enable WPU

strt:
wpu=%00001000      ;enable WPU on GPIO.3
pause 500
wpu=%00000000      ;disable WPU on GPIO.3
pause 500
goto strt
end

OK, I now this is not work. I also now the GPIO.3 WPU is activatable only via
MCLRE, the GP3 pull-up is enabled when MCLRE is set to"1" in the configuration word register, and disabled when MCLRE is set to"0".

How It works in PICAXE, thats the question. Does anyone have an idea?

Louis

[Ioannis]

can you post also the fuse configuration?

Ioannis

[louislouis]

Hello,

in PICAXE no need to use any config.

In picbasic I use this:

#CONFIG
__config _INTRC_OSC_NOCLKOUT & _WDT_OFF & _MCLRE_OFF & _CP_OFF
#ENDCONFIG

But I also used this:

#CONFIG
__config _INTRC_OSC_NOCLKOUT & _WDT_OFF & _MCLRE_ON & _CP_OFF
#ENDCONFIG

[Ioannis]

The weak pullup on GP3 is enabled only when MCLR is enabled.

You may try also ANSEL to set it to

DO
ANSEL=0
PAUSE 500
ANSEL.3=1
PAUSE 500
LOOP

This will enable and disable the weak pullup.

Ioannis

[louislouis]

The weak pullup on GP3 is enabled only when MCLR is enabled.

You may try also ANSEL to set it to

DO
ANSEL=0
PAUSE 500
ANSEL.3=1
PAUSE 500
LOOP

This will enable and disable the weak pullup.

Ioannis

tried, not working. ANSEL.3 is for pin GP4 not for GP3.

[Sherbrook]

Try setting GP3 to input as setting to output turns off weak pull-ups

[louislouis]

GP3 is setupable only as input.

[Ioannis]

OK, then this would only work if one could change the MCLR bit in config word, address 2007h.

But this can only be accessed in Programming the chip...

Interesting one!

Ioannis

[Dave]

GP.3 is only configurable as an added input pin when nor being used as the RESET pin. NO output configuration is possible.

[louislouis]

yes, if I configure the MCLR bit in config word to "1" then the LED is ON because the transistor is open via internal pull-up. If I configute the MCLR bit to "0" then internal pull-up is disabled and the transistor is closed because the 1M resistor is pull the base to ground.
That's work, but how to do that in program I don't know. However, it must work somehow, because in PICAXE environment it works.

[richard]

how sure are you that a picaxe 8m2 is a 12f683

this makes me doubtful a 12f683 pegs out at 20mhz