so i'm setting up the ISP header for my board..
what should i do with the power pin?? is it okay to just tie that to the output of the voltage regulator that powers the mega128?
I think that is ok, but it depends on your programmer though. If your programmer supplies power to the target than you should make sure that your target supply is off. If it isn't you can leave the VTG pin unconnected on the ISP header. You could of course incorporate the means to disable the connection between VTG on the board and the programmer, by for example a PC-style jumper. to make it more versatile. Correct me if I'm talking jibberish anyone.
I'm not sure about he programmer.. i'm using pony prog to program, and using winAVR as the programming enviornment and compilier
so what i'll do.. is have a power pin connect via a jumper.. but wheni first program it.. i'll just remove the jumper and see if it programs.. if not.. then i'll add teh jumper..
sound like a good plan?
What I mean is that if connecting the VTG from the header to the output of your target board regulator you shouldn't power on the target board if your programmer supplies power via the header, this to avoid possible problems.
On the other hand if your programmer doesn't supply power via the header it shouldn't matter, but to be on the safe side you can do the jumper thing to be able to break the connection between VTG on the programmer side and the VTG on the board. In this case you obviously power your target via the regulator.
On some programmers such as the AVRISP/AVRISPmkII, it is critically important that the VTG pin must be connected to the output of your regulator, since the programmer will then use that voltage to determine the proper voltage levels to act as logic thresholds on all the other signal pins.
thanks for the replies. I'm using a programmer i bought from sparkfun.. I have both the parallel and serial ones
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