04-02-2019 06:05 AM
There are three FPGAs which are connected in JTAG chain.There is an issue with third FPGA. On adding third FPGA none of the devices are detected on JTAG. If we remove third FPGA from the chain, other two FPGAs are detected.Observations are given below for
Case 1 : Inserting all the FPGAs on chain
Case 2 : Third FPGA is removed from the chain
04-02-2019 08:50 AM
This issue could be related with the JTAG signals. Check in the third FPGA the JTAG signals( voltage level, waveform). Let me know if this help you.
04-02-2019 03:11 PM
Insert the third FPGA and be sure that the JTAG signals aren't short-circuit.
Check that there's not a low voltage level in the JTAG signals when you connect the third FPGA, check also the JTAG waveform.
If you can share a screenshot of the JTAG signals better
04-02-2019 11:17 PM
Checked the voltage level. They all are having expected voltage levels, i.e 1.8V.
I have attached the screenshot of JTAG signals below :
04-03-2019 05:24 AM
I see the screenshots and the clock signal exhibit some distortion. If you can, take a screenshot of the TDI and TDO signals also. Can you replace the third FPGA by another or interchange this FPGA with another that you are sure that is OK? ESD could be a reason of this problem.
04-09-2019 03:48 PM
Are all 3 Xilinx devices?
If not, please take a look at this Answer Record:
Let us know what's in your board, maybe a diagram of your JTAG chain?