I'm about to attempt building my own basic GAL programmer after doing much reading on the web. But first, I've got me a few questions!
1.) For starters, why do GALs use all different programming voltages? Is it based on the chip model? Is it based on the company who made it? Both? Seems like it would have made more sense to just design them for a standard voltage, much like how apparently 12v is the standard to read their contents. Though maybe that'd have made them more expensive, I dunno. Or maybe they did it on purpose so you'd buy their programmers/software?2.) Does going above the programming voltage by the fractions of volts by which a programmer can increment actually kill the chip? Cause they seem to be rather small increments.
3.) Why are the programming voltage and timings stored in the PES, when from what I understand the PES is erased when you do a chip- erase? I guess this means you have to make sure you read the PES out first and save it, then write it back in after writing in your new fuse settings, and hope nothing goes wrong in the meantime to lose that configuration info.4a.) Since I don't have a bench power supply, I'm going to have to try to make do with something else. Would it be possible to use something like a 7805 with a potentiometer on its ground, powered by maybe 18-20v (whatever AC adapter I can find), to generate the programming voltages?
4b.) Is it even safe to run an '05 much higher than its standard output?4c.) How does that affect its current output? And relatedly, am I right in the assumption that the higher the output voltage (getting closer to the input voltage), the cooler the '05 would be?
4d.) Would I need a resistor temporarily across the output of the 7805 to properly test its output voltage with a multimeter? Since I assume the voltage might differ when connecting the meter directly compared to when the '05 is connected to the chip and erasing. If it's as sensitive to the voltage range as I've assumed, then I'd have to make sure the voltage I generated was very accurate and all.Forgive my latter questions if they sound dumb, but there's still much that confuses me when it comes to "analog" electronics, as opposed to digital circuits. But I'd appreciate any help anyone can offer!