Reading Port A

[stma]

Hi, This could be a pic problem or a code problem.
I am trying to write a value to port A then read it back and display the value on screen. code below.

void TestFunc()
{
#byte PORTA = 5
#define ALL_OUT 0
#define ALL_IN 0xff

int i;

set_tris_a(ALL_OUT);
porta=0x0a;
set_tris_a(ALL_IN);
i=porta;
printf("%x \n\r",i);
return;
}

I have tried other ways but get the same problem.
Setting the port up is no problem, the correct byte is placed on the pins. The problem is when I try to read, all the pins go high!
Any help appreciated.
Thanks
Steve

[Mark]

What do you have connected to the pins?????

You do realize that

[stma]

Thanks for that. Good point about reading not neccesarily what i wrote. It is really a test routine. I am writing a byte to a cpld to set a multiplexer address. Then I read data in from another pin (well thats the plan)
Im off to do a bit more thinking!!
Thanks again
Steve

[Ttelmah]

Add, that unless you specify #use fast_io(A), the compiler will already be adding the equivalent to the two set TRIS functions for you. This will be adding to the duration from the moment the output is written to the pins, and the attempt is made to read them.
If you want to read what is currently being output on the pins, use #use fast_io, set the pins as outputs, and write the data pattern, then leave the pins as outputs, and read the input. The input function will work, whether the pins are operating as outputs, or as inputs, but in the latter case, the signals are not driven by the chip when the reading is made.

Best Wishes

[Mark]

[Ttelmah]

I think I'd say, that technically, it does 'always work', but it reflects the real status of the pins, rather than what you are trying to drive them to. Assuming the original poster is trying to actually test whether the pins are going to the pattern required, then this would be what was wanted.
It is an important 'caveat' though, especially if the instructions are done quickly one after the other, where the capacitance of the pins can prevent them from havin yet reached the required target voltage...

Best Wishes

[Mark]