cant pgm fuse bit??

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I want to program the rcen fuse bit on a at90s1200 to use the internal oscillator. I have the stk200 connected via parallel port, and the latest version of AVR ISP. All the fuse bit controls are grayed out so I cant mess with them. please help

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I also cant flash some 1200s that i just got from digikey,All I have is a serial programmer. I beleave the fuse bits are set because when I ID the chip I get 01 02 03.Can these be rest and how? thanks

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I believe the stk200 can only program devices in serial mode, and the RCEN fuse in at90s1200 can only be programmed in paralell mode. therefore the fuse bits are greyed out. To program the fuses use a paralell programmer, e.g. stk500.

rgds
bjorn

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If your 1200s have their RCen fuse programmed (running on internal RC osc) the serial programmer may be trying to program the 1200s at too high speed. If the parts are marked 1200A they are shipped with this setting.

The programming clock must have a pulsewidth (clock high time) of at least 4 clock cycles of the 1200 main clock. Running at internal RCosc this means that the programmer must not clock data faster than 250KHz (at 50% dutycycle). Try measuring the frequency of the SCK signal from your programmer. To overcome this problem the programming speed must be reduced or the RCEN fuse cleared by a paralell programmer.

hope this helps.
rgds

Bjorn

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Thanks for the tips. Guess I cant use the internal oscillator then without building a parallel programmer :(

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I suppose the quickest solution is to get yourself one of those STK500's. I have an STK200 and I also failed at doing so, but with STK500's high voltage parallel programming it did it without refusal. Besides, there's lots of things on that STK500 that's worth upgrading for.

Dave

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