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AR# 16058

5.1i iMPACT - IDCODE looping fails with "ERROR:iMPACT:1210 - '1':Boundary-scan chain test failed at bit position '1'"


General Description:

The user is able to connect to his/her programming cable, but an idcode looping test to verify that signal integrity is intact fails. The error message that is reported is as follows:

"ERROR:iMPACT:1210 - '1':Boundary-scan chain test failed at bit position '1'. A problem may exist in the hardware configuration. Check that the cable, scan chain, and power connections are intact, that the specified scan chain configuration matches the actual hardware, and that the power supply is adequate and delivering the correct voltage."


This error, which signifies that the first bit read out on TDO is invalid, is nearly always due to a signal integrity problem. The error essentially indicates that either the power source is not compliant with power requirements (it supplies an incorrect voltage or is incapable of providing the necessary current at the required voltage level), the board connections are incorrect, or a disconnect has occurred in one, or more, of the nets connecting to the device JTAG pins.

To debug this error, first ensure all devices in the chain are defined. (i.e., IR length is specified correctly for non-Xilinx devices). Then disconnect your programming cable from the board and device under test and probe the cable pins using an oscilloscope or logic analyzer to ensure that the cable is indeed behaving as expected. Expected behavior for the IDCODE looping sequence is outlined in the software manuals --> iMPACT User Guide --> Troubleshooting for Boundary-Scan Chains --> Boundary-Scan Chain Debug. A good way to ensure that your cable is working correctly is to also use the "Debug Chain..." functionality under "File" in the Impact menu bar. This feature will allow you to apply known voltage levels to TDI and TMS to ascertain proper functionality.

Now, with the cable still disconnected and power applied to the device under test, probe TDI and TMS; both should be at a logic "high" since they're pulled up internally. Note that Vref must be connected to a reference voltage for this to hold true. If TDI and TMS are not at "high" as expected, you likely have power problems. Now, reset the cable by using Output --> Cable Reset in Impact and connect it to the board and device under test again. Use the "Debug Chain" feature once more to drive TDI and TMS both low and high and probe the device under test pins to verify that they take on the expected voltage values. If not, then you have a disconnect between the cable and device, or possibly the net that connects the two is inadvertently shorted to ground or Vcc. If you suspect, to provide an example, that the net is shorted to ground, you can test that notion by powering down the system and measuring the resistance from the net in question to system ground. If all is well, such a test should yield a high resistance value (likely MOhms).

Finally, if all tests are inconclusive up to this point, then perform the idcode looping operation again with everything connected. Probe TCK to ensure you have a valid, clean clock signal, probe TMS to verify that it's toggling, and probe TDO to see that it also toggles. The Impact Guide in the software manuals, as referenced above, provides details about what the toggling waveforms should look like. If everything is functioning as expected, but TDO isn't toggling, then the device under test may be faulty. If TDO is, indeed, toggling, but you still get the software error this solution addresses, then if you need assistance, please open a WebCase at:


AR# 16058
Date Created 09/03/2007
Last Updated 12/15/2012
Status Active
Type General Article