Okay, I've designed a small board targeted at giving people some SMD soldering practice. It's got an SOIC-14, some SOT23-3s, 0805 resistors, 0603 capacitors, a tactile switch, etc. -- so far so good. I built up the prototype yesterday and aside from a stupid reversed footprint everything works just as expected... except programming. The board is based around an AtTiny24A and is designed to use ISP for programming. I've been able to program it, but it's flaky; very flaky. Not only has it failed to read the signature properly ( intermittently ) but it has actually failed to read and write properly after a successful signature verification. I haven't slowed the bit clock as much as I could ( I'm the chip at 1MHz, IRC @ 8MHz and CLKDIV8 enabled ). I have made sure that I'm below 250kHz though.
I've never had these sorts of issues with programming an avr, it either works or I've wired it incorrectly -- not this time. The problem seems to be that the RGB LED on the board is being driven by mosfets that are tapped from two of the programming lines ( I don't have access to an o-scope to check the waveforms unfortunately ). The fets I'm using have a gate capacitance of 40pF ( worst case ). Is that too much ( obviously... ).
So the question, since I have to respin the boards to fix the footprint foible anyway, do I insert resistors in series with the fet gates, or do I just give up those pins and play it safe? Thoughts?
Martin Jay McKee