fpga missing in jtag chain

thepiper · Sep 27, 2009

hi, i have developed a spartan ii board, and i have a problem configuring it. when impact tries to detect the devices on the jtag chain, which contains a prom and the fpga, the fpga is missing, and ofcourse all programming commands to the prom fail (idcode problem), what could cause this problem?

farhada · Sep 27, 2009

Try to slow down your JTAG clock, you may have noise problem in your JTAG chain, this is a very common problem causing the failure of JTAG interface.

The second thing to look is to see if the pull-ups and pull-downs for the JTAG signals are connected correctly.

Xilinx used to have these recommendation for their CPLDs that maybe a good starting point for problem solving for you:

• Make sure VCC is within the rated value: 5V ±5% for XC9500/XL and 3.3V ±10% for XC9500/XL.
• Provide both 0.1 and 0.01 mF capacitors at every VCC point ofthe chip, and attached directly to the nearest ground.
• Use the latest Xilinx download cables. This would be a ParallelCable with serial numbers greater than 5000 or any X-Checker cable.
• Consider including buffers on TCK and TMS interleaved at various points on your JTAG circuitry to account for unknown device impedance.
• Always be certain to use the latest version of the Xilinx JTAGProgrammer Software.
• Put the rest of the JTAG chain into HIGHZ when programming a troublesome part.
• If free running clocks are delivered into the ISP CPLD, it may be necessary to disconnect or disable their entry into the CPLD while programming.
• If 9500/XL is last in a JTAG chain, attach the download cables red VCC lead to the 9500/XL VCCIO.

Best regards,
/Farhad Abdolian

fpga missing in jtag chain

thepiper

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farhada

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fpga missing in jtag chain

thepiper

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