stk500 problem....

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#1
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Yeah, I know, this subject has been beaten to death a million times already.
I've searched the forums, and I haven't found anything quite as strange as this.
Ok, so I build a PC board and ISP'ed my program to an ATmega16 with the STK500.... tested the board, everything works fine. Now, several weeks later, I want to change the program on the chip. Can't enter programming mode. However, the current code in the chip runs just fine when I apply power to the board, the STK500 is fine (I've programmed other chips with it).... physically the board is perfect, all traces intact, etc.
Is there anything else that could be messed up, or am I going to have to assume the ISP circuitry in the chip died somehow and replace it?

bluefire211

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Are any of the port pins used for ISP being *driven* by other devices in your
circuit, that would conflict with the stk signals during programming?

Tom Pappano
Tulsa, Oklahoma

Tom Pappano
Tulsa, Oklahoma

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Nope, all ISP pins are dedicated to that. They don't connect to anything else.

Also, I have a 47k pullup from VCC to Reset.... the STK500 seems to be able to drive a 47k pullup just fine.....

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Hi,

Is the Mega16 in the STK500? If so try parallel programming - maybe some fuses got changed to bad values.

Also check the frequency of the STK500's on-board oscillator - as this frequency sets the programming frequency, and this frequency should be similar to the clock source of the AVR.

-Colin

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Ok, well, the MCU seems to not respond to a reset by manually pulling down the reset pin.... so I think either I set the reset disable fuse (I highly doubt that though), or I fried the reset circuitry in the chip. Thats reasonable, since I don't have a protection diode on it....
Oh well, for those in the future who have this problem.... put a protection diode on your reset pin! They don't have one internally.

Good thing I *really* love removing TQFP's by hand.

Over and out,
bluefire211

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If you ever lose your *love* for TQFP rework, check out the hot-air SMD rework station from CircuitSpecialists.com. For about $180 US you can have pro tools.

I didn't used to like TQFP rework, now I do.

Of course, if you don't do it often, then ChipQuik is a good solution too.

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Hi,

I also got a hot air station (http://www.web-tronics.com/esdsasmdrest.html), its great. I did SMD by hand for a while, but after my hand soldering iron broke I decided to just get a hot-air/hot-metal station.

The main thing it makes easier is *removal*, that is WAY easier with hot-air.

-Colin