JTAG with multiple ATMEGA64

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#1
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Hello all,

has anyone experience with emulating more than one ATMEGA in a JTAG chain?

I use 5 pcs. of ATMEGA 64 in a JTAG-chain. Now I want to debug these controllers (one after another) with the ATJTAGICE. In the AVRSTudio I can set any options (Debug / JTAG ICE Options / Connection). There I can check the box "Target device is part of a JTAG daisy chain". If I activate this option I have to define 4 values about the devices before and after my target and about the instructions bits before and after. Here is my problem. I have only 5 ATMEGAs in the JTAG chain. But what are the values for the the instruction bits febore and after? I cannot found any hint in the datasheet. Can anyone help me??

Thank you very much for your help. With best regards and the best wishes for a good and peaceful year 2004!

Winfried

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There are 4 instruction bits per device, so if you want to talk to your third device you write 8 instruction bits before and 8 after.

-Geir

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I am trying to do something very similar with two Mega32's but I don't understand how this chain is connected, does the TDO from the first device to the TDI of the second and the loop forms like that?

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If so is it possible to have two instances of AVR Studio open at the same time, I am trying to debug an interface between the two controllers and finding it a pain to have access to separate JTAGs at the same time.

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henrywood wrote:
I am trying to do something very similar with two Mega32's but I don't understand how this chain is connected, does the TDO from the first device to the TDI of the second and the loop forms like that?

That's the way multi-JTAG normally works - it's a line of shift registers effectively. If you want to get the data from B then you have to say how many clocks are needed to shift A's data out of the way first.

Cliff

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I haven't done such a thing yet. But I'm interested. Is there still a possibility to program the avrs in a multi part jtag chain? Also with different parts mixed (e.g. atmel + altera)?