UC3B design JTAGmkII communication stability problem!

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Hi,

I just got my new UC3B0256 PCB design, and I'm testing it now.

In my design, I also used TDI,TDO and TMS as GPIO pins and they are connected to a level translator IOs, and the level translator can be disabled (when the level translator IO become high-Z) by another GPIO.

I got some strange comunication stability problem for my JTAGmkII interface. A lot of times after I downloaded the program and unplug the JTAG connection, and program works, and after some time connect it back again and try to talk to it in AVR32studio and then there is no connection and it just give me a lot of JTAG errors. It seems the PCB always needs to be completely unpowered for a little while before the JTAG communication works again.

I'm sure that my JTAG interface logical connection is correct. But just wondering what happens when the program I downloaded is using TDI,TDO and TMS, and AVR32studio starts to talk through JTAG? Will it always reset UC3B first and then try to enter the JTAG mode?

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any one knows?

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But if you asked them to be somthing else than jtag pins i assume a reset/reprogramming/power off is needed to get then back into jtag mode ??

Maybe i dont understand you question.

Do you have schematics ?

/Nicholas

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the strange thing is if I get the JTAG connection to my PCB, then I can always download new program correctly and program works afterwards, and as long as I don't unplug the JTAG connector, I can always reprogram my PCB without any problem. But if I unpluged the JTAG conenctor after I downloaded new program, and after sometime if I plug JTAG onto PCB again, then it could give me errors for connecting to it.

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I connected TDI, TDO and TMS pins to bidirectional level translator txb0108, which is enabled by PA30 pin on my design. If I connect my JTAG adaptor to ths PCB, then PA30 would have a 10K pull-down resistor.

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Just speculating here since I dont have any doc at hand know.

But when you unplug the jtag conn inputs will float. TDI,TCK,TRST#,TMS

question is if you pull them up/down on the input to the level translator in same way as where it normally works ?

/N

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i just have 10K pull-up for TCK pin. The TDI,TDO and TMS pins have no external pull-up or pull-down on my PCB, I use them as GPIO outputs to the level translator.