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Altera_Forum
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11 years ago

Detection problem in JTAG with MAX7000S

Hello, i'm newbie with FPGAs programming. I'm trying to use JTAG on a Max7000S (exactly an EPM7160STI100), without satisfying results.

When i try "Auto Detect" fonction i have this message "Unable to scan device chain. Can't scan devie chain".

So, i try the JTAG Chain Debugger,"Test JTAG chain" and...

JTAG chain problem detected

No device detected

The TDO connection to the download cable might be shorted to VCC or is an open circuit

The TCK and TMS connections to the last device might have problem

When i look TCK, TMS, TDO and TDI on scope, i have some correct signals on TCK, TMS and TDI, but only 5V constant on TDO, is it normal?

I have a pull down for TCK, three pull up for TMS, TDI and TDO. Resistors of 900ohm.

If you have proposition, i take it !

1 Reply

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    11 years ago

    Try removing the pull-up resistor from TDO (it shouldn't need it anyway).

    900 ohms is too low for my liking. Refer to the 'pull-up and pull-down of jtag pins during in-system programming' section of an-100 (http://www.altera.com/literature/an/an100.pdf) for guidance.

    If it's the only device in your JTAG chain you shouldn't need any pull up/down resistors.

    Cheers,

    Alex