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Altera_Forum's avatar
Altera_Forum
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17 years ago

Unable to scan device chain

Hi all,

I´m relativ new with the CPLD´s, and now I have the first problem with programming the device. It´s a EPM570T100.

I ´m using a Elcamino PICoMax to programm the device. This works with one of my boards, so the programmer seems to be o.k. But I have another board which has always this error message when trying to Auto-detect:

Unable to scan devive chain. Can´t scan JTAG chain......

I checked twice every pin, VCC, GND and the 4 JTAG pins... no error found. I also measured with the Scope at the 4 pins. I see a signal on all 4 pins, but I´m not sure if they are right...

My three questions:

Any ideas what my problem is?

What do I have to see at this pins?

How do I use the debugger to find the error?

Richi

4 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    17 years ago

    What devices are in the chain on the board that doesn't work ? Do any devices have a TRSTn pin ? If so, this pin normally requires to be held low for normal operation and raised high for JTAG chain. Holding it low will break the chain.

  • Altera_Forum's avatar
    Altera_Forum
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    17 years ago

    Hi, No other devices in the chain.

    But I fixed it:

    1. My Laptop seems to have problems with the parallel port. The other PC works now

    2. I had to put more caps to the supply. 4x 100nF are not enough. Now I have 6x 1µF and it works!
  • Altera_Forum's avatar
    Altera_Forum
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    17 years ago

    Good diagnosis

    I've also had problems with ground loops and laptops. Some (perhaps older) laptops have 2-pin mains adapter connections, which means there is no earth. So a substantial AC leakage current can run round the JTAG circuit ground if the DUT is properly grounded. There are at least two ways to fix this: 1 get an AC adapter with a properly connected ground; run a substantial ground cable from the parallel port to the DUT's ground.
  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    Just solder 4 x 10nF Capacitors from all 4 Data/Clock wires to ground and everything is fine!