[solved] crazy about pin RA4 in PIC18F4550

potato · Joined: 23 Mar 2014 Posts: 16

Hi again!

I've been doing some research here on the forum and I think I'll soon become crazy... My PIC ignores the inputs coming from pin A4 (I have a button there and there are no bouncing problems).

I thought I saw some light when I came across a couple of threads talking about #fuses NOIESO and #fuses SOSC_DIG or DIGITAL... but my compiler (version 4.0, though I've tried it with version 4.1 and it doesn't work, either) doesn't recognise the second fuse, neither SOSC_DIG or SOSC_DIGITAL.

I have to use this pin because the others are occupied (or not working, as A5, C1, C4, C5 or B7). It's not a PIC's problem, because I bought a new one and it's just the same...

What can I do? The fuses are the following:

Humberto · Posted: Sat May 17, 2014 9:29 am

Some questions:

1) Does your hardware successfully passed the basic test of a blinking LED?
2) If so, did you check if the LED blinking period corresponds with the code?
3) How is connected the button in A4?
5) Did you add a 10k pull-up resistor with the button?
6) Are you aware of this fuse set?

dyeatman · Joined: 06 Sep 2003 Posts: 1941 Location: Norman, OK

In addition to what Huberto said....

Since we cant see the rest of your code we have to guess.
Did you disable ADC?
Did you disable CCP?
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Ttelmah · Joined: 11 Mar 2010 Posts: 19589

That fuse is for PIC's like the PIC24's. Your chip doesn't have it.

Read the data sheet:

"The RA4 pin is multiplexed with the Timer0 module
clock input to become the RA4/T0CKI pin. The RA6 pin
is multiplexed with the main oscillator pin; it is enabled
as an oscillator or I/O pin by the selection of the main
oscillator in Configuration Register 1H (see
Section 25.1 “Configuration Bits” for details). When
not used as a port pin, RA6 and its associated TRIS
and LAT bits are read as ‘0’.
RA4 is also multiplexed with the USB module; it serves
as a receiver input from an external USB transceiver.
For details on configuration of the USB module, see
Section 17.2 “USB Status and Control”.

The command to disable the T0CKI use, is:

setup_timer_0(T0_INTERNAL);

If you are running, you need to be running with the internal transceiver, otherwise the hardware uses this pin.

potato · Joined: 23 Mar 2014 Posts: 16

hi guys, thanks for you super-fast replies! Very Happy

I'm afraid I had no reasons to turn crazy... I've realised I had a software problem, because I had a while loop to wait for a button to be pressed and I didn't write that it also had to wait for a4... (because I had it in another while loop)

I know how stupid it sounds, specially because I had review the code millions of times Embarassed

Anyway, thanks for the ideas and, Ttelmah, thanks for specialising that I don't have to worry about that pin!