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Problems with Port A on a PIC16F877

 
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jfk1965



Joined: 21 Oct 2003
Posts: 58

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Problems with Port A on a PIC16F877
PostPosted: Wed Apr 25, 2007 1:59 am     Reply with quote
compiler Version 3.245

I have the port set to read adc on channels 0 - 3 using
Code:
setup_adc_ports(AN0_AN1_AN3);


as it states in the device header file. This works ok no problems, the problems are that I want to use Pins RA4 + RA5 as outputs to drive an LED. These pins are permantly in the low state even when I use a command
Code:
output_high (Pin_A4);


Is there any reason for this that anyone can suggest?

TIA

JFK
PIC_ECM



Joined: 23 Apr 2007
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PostPosted: Wed Apr 25, 2007 2:31 am     Reply with quote
Confirm that you hav'nt set all of port A as an input. That may be the cause of your problem

Carlos.
jfk1965



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PostPosted: Wed Apr 25, 2007 2:44 am     Reply with quote
Hi Carlos

No I haven't set it all as input it works fine if I use the MPlab SIM Debugger but doesn't work on an actual pic.

JFK
ckielstra



Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands

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PostPosted: Wed Apr 25, 2007 3:40 am     Reply with quote
As on most PIC processors pin RA4 is an open-drain output. For example you can add a pull-up resistor to get a high level output voltage. In your case, driving a LED, I would reverse the LED connection and connect the cathode of the LED to the PIC (PIC sinks current i.s.o. sourcing, ouput_low() will light the LED).

Pin RA5 is a normal output and should work as expected.
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