Help. PIC16F874A board not working at all

If this is a breadboard design, are you sure the oscillator starts running properly?

I'd first configure the PIC to use an external RC osc, disable WDT, and enable power-up reset timer (no external reset connected). After programming and removing the programmer, you can watch the R&C voltage with an oscilloscope, see if it runs...

Also are you sure the ALL-100 really supports the PIC16f874A? (correct config word etc)

- Jan

Thank you. It is designed on universal printed circuit board. I just used a crystal and two capacitors for the oscillator circuit. ALL-100 supports PIC16f874a, but I'm not sure whether the default configuration is working. As I said, the default configuration performed PROTECTION as its last process. But when I checked again (by reading or comparing the contents), I just found nothing was actually written. After I tried without protection, code seemed been written correctly.

- chess

When you enable "code protection", this means you can't read it back from the chip. So what you saw is ok. That's the point of code protection :-)

- Jan

Hi.

Some suggestions: AFAIK "protection" means code protection, so you don't see, what's written. It's not so easy handling, if you enable code protection (CP) while programming. If some start problems, it's generally a good idea to minimize the configuration, simplest OSC mode (internal or RC), no watchdog, no brown-out, no MCLR if possible, debug off and power-up timer on.

To your code: It is a bad thing, to manipulate bits on the i/o ports with bsf/bcf/and/or/ ..., because all operations are read-modify-write operations. So if you change one bit, some others can be influenced from external. For example in your code, if B0 is connected with a resistor to ground, the next operation on B5 will also set B0 to low. Therefore I recommend, to change the bits in a other register and write the whole byte to the port register. In the next generation PIC (18F) there is a special register (LATx), to prevent this case.

HTH Michael

Dear chess,

chess schrieb:

Your code does not contin any configuration register settings. See __CONFIG command and the processors datasheet. Since most assemblers set all the config bits 1 by default, you select RC oscillator mode, which is probably not what you want.

For a test circuit, tieing MCLR to Vdd is okay.

Using a scope, watch pins OSC1/CLKIN and OSC2/CLKOUT. If the PIC is running, you'll notice an oscillation on at least one of these pins.

Yes. You didn't set the configuration bits.

HTH Wolfgang