RA.4 Open collector,...

[tazntex]

First thing, yes I did search the forum on this question although I was certain I already was correct in my thoughts about ra.4 on my 16F628A. Melanie makes it quite clear especially with this post:
http://www.picbasic.co.uk/forum/showthread.php?t=1642

BUT!!!, Using and led with a resistor on my anode going to 3.3V and my cathode to ra.4, does not work, change processors and programmed with my replacement of the pickit3, my new favorite, the pickit2. I think I even made it as simple as possible with this code:

DEFINE OSC 4
CMCON = %00100101
VRCON = %11101100
PAUSEus 10
TRISA = %00000110
TRISB = %11110001
PORTA = %00000000
PORTB = %00000000
OPTION_REG.7 = 0
OPTION_REG.6 = 0
rf var porta.4


main:
low rf
pause 500
high rf
pause 500
goto main

And it still doesn't work. But I did move the cathode to ground and yes the led lit, so the led does work.

Anyhow, this may have sounded like a stupid question but If I don't ask, I'll never learn anything
Thanks again especially for all the knowledge I have gained here on this forum.

[tazntex]

I have it working with this code:
DEFINE OSC 4
CMCON=%00000111
VRCON = 0
PAUSEus 10
TRISA = %00000110
TRISB = %11110001
PORTA = %00000000
PORTB = %00000000
OPTION_REG.7 = 0
OPTION_REG.6 = 0
rf var porta.4

main:
low rf
pause 500
high rf
pause 500
goto main

Does it have something to do with me using the comparator on ra.1,ra.2? I have been reading the datasheet and it mentions ra.3,ra.4 in section5.1 PORTA and TRISA Registers, I am already using ra.3 with no problems as an output.

[gadelhas]

Hi;

Try this;

1 - Connect the RA4 Pin with the resistor to VCC;
2 - Connect the anode of the led beetwen the resistor and the RA4 Pin;
3 - Connect the Cathode of the led to GND

And post the result

[rsocor01]

The reason that you need a resistor between RA4 and Vcc, like Gadelhas mentioned above, is because RA4 in that chip is an Open Drain (OD) type.



Robert

[tazntex]

Sorry about the delay getting back to ya'll. Ok, your instructions said:
1 - Connect the RA4 Pin with the resistor to VCC;
2 - Connect the anode of the led beetwen the resistor and the RA4 Pin;
3 - Connect the Cathode of the led to GND

with or without step 2 the led is illuminated.

Thanks for the fast response.

[Bruce]

RA4 is C2OUT with the 1st configuration you had so you couldn't use it for a digital output. With comparators disabled you can.

This should work fine to drive your LED on RA4 ---|<|---/\/\/--VCC.