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Altera_Forum's avatar
Altera_Forum
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14 years ago

Max V JTAG Daisy Chain

I'm implementing a JTAG Daisy Chain for the first time on a PCB. Previously, on a prototype board I had two headers for JTAG programming but I'd like to utilize a daisy-chain configuration to reduce ...
Altera_Forum's avatar
Altera_Forum
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14 years ago

Understood on the series resistors. I'll go with 50 Ohms.

Stupid question: how does a buffer help with reflections? I'll probably go with the same buffer you went with: NC7WZ16P6X. It's quite cheap and tiny.

And if I understood the schematic correctly, I put this between the header and the first CPLD in the chain and the TCK and TMS signals diverge from there on and goes to two CPLDs.

Or perhaps I misunderstood you. Did you mean to say that I should use a buffer per CPLD? I.e.

TCK from header ----> Buffer# 1 ---> CPLD# 1

TCK from header ----> Buffer# 2 ---> CPLD# 2

Same applies to TMS, TDI and TDO on its way back before it enters the header again. I can see how a buffer would help with transmission line effects in this case but not the previous one. The buffer would isolate the signals from each other and so reflections won't be an issue(?).