16F877A won't keep relay on 100% of the time

[Rob]

I have this assembler code at the start of my program:

@ DEVICE HS_OSC, WDT_OFF, LVP_OFF, BOD_OFF, PWRT_ON, PROTECT_OFF

I'm quite certain the "WDT_OFF" turns the Timer off.

Yeah that's right, it does turn the tmier off.

The "HS_OSC" is my change because I have a 20Mhz xtal, and yes, I have "OSC 20" in my "PIC Basic" code.

It still sounds to me like the PIC is resetting or some other code elsewhere in your program is causing the output to go low on the pin you are using. Just for arguments sake, create a new program with just this code and try it out.

The other line items are "Boiler Plate" I've found looking around the Forum.

I've never heard the term "boiler plate" before so I'm not quite sure what you mean?

Cheers

Rob

[peterdeco1]

Try removing the relay and use an LED with a resistor. If the LED works, your code is OK and the relay coil is the culprit. I've had interference problems with small vibrating motors located very close to the PIC.

[Acetronics2]

Hi, Coyote

1) Did you try to use HIGH Portx.y ...

I noticed many times it is much more reliable than Portx.y = 1 in disturbed circuits ...

2) @ 20 Mhz, you also could try PULSIN instead of count ( as it is a square wave )... nominal result will be 20 ... and there will be a little less "rollover" issues ...

3) The ideal way would be to use the "capture" feature of the CCP modules ... in a '877 there are two modules !! ...

Darrel's instant interrupts are ... the easy way ... to make that. And it takes much, much, much less CPU time ...

Alain

[Rob]

Hi, Coyote

1) Did you try to use HIGH Portx.y ...

I noticed many times it is much more reliable than Portx.y = 1 in disturbed circuits ...

That's interesting! I learn something new every day! Nice one!

Cheers

Rob