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Altera_Forum
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17 years ago

Jtag problem

Here we go again! For a very simple project i used a MAX7032S. Suggested pullup an pulldown are used at jtag pins, connections kept as short as possible and large ground path as well. Only way...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
17 years ago

Hi OrchestraDirector !

It's a custom board that use to control camera. It configured good at the beginning (about 50 times), then I can't access jtag. I have got 4 circuit boards. Among them, 2 boards died jtag port (config many times) and 2 board still operates good (use rarely). I checked waveform of jtag port on bad and good boards by oscilloscope. I see that, the waveform amplitude of TCK signal is reduced on bad boards, i measured impedance on TCK pin of bad boards and good boards. It followed :

1st bad board : 50 ohm.

2nd bad board : 62 ohm.

3rd good board : 992ohm.

4th good board : 992 ohm.

about config circuit, I used from other circuit (it still operated good). I can't understand why it damaged jtag port ? this is my config circuit :

I didn't used pull up resistor on TDO pin (follow altera guide).

Thanks in advance !

http://www.cavepic.com/image-1219_4935ead3.jpg

http://www.cavepic.com/thumb-1219_4935ead3.jpg (http://www.cavepic.com/share-1219_4935ead3.html)