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Altera_Forum
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12 years ago

JTAG TCK droop using USB Blaster(Ver B) and Cyclone II

I have a NIOS-II processor in a Cyclone II which I am trying to debug using a USB Blaster (Ver B.) cable and The NIOS-II eclipse tools. However, the JTAG communications are highly unreliable. ...
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Altera_Forum
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12 years ago

Good call !

I found that a 22pF capacitor between TCK and ground, right next to the FPGA pin has done the trick.

It looks like the USB Blaster 'B' has a very weak drive arrangement for TCK. (maybe a 470R series output resistor, and then a 1K pull-down resistor ?)

Maybe it was picking up noise from somewhere along the 2" of PCB track from the connector to the FPGA, or the 8" of jtag cable attached to the USB Blaster.