I'm trying to find out what could cause a pin in a Virtex 300 part to short out. It's happened more than once, within a week's time frame. I can't really find any material on Xilinx's support web site about this situation (and what to look for).
Work-around for the first one was to lift the pin off of the board and re-route the signal to another pin (used one adjacent to the bad one). May end up doing the same thing for the second pin now.
Any suggestions welcomed...
-bob
Be more specific: short to gnd or Vcc ? What is the remaining impedance?
If it is really low ( 5 Ohm, then it might be the drive transistor permanently turned on. You might also test it for impedance when Vcc = 0
This is not an explanation or a cure, but a way to categorize and thus clasify the problem. Peter Alfke
Be more specific: short to gnd or Vcc ? What is the remaining impedance?
If it is really low ( 5 Ohm, then it might be the drive transistor permanently turned on. You might also test it for impedance when Vcc = 0
This is not an explanation or a cure, but a way to categorize and thus clasify the problem. Peter Alfke
Bob,
In addition to Peter's questions, make sure your pins are assigned per your intentions. Check the pin report after you run PAR. Pins that aren't assigned (constrained) could end up anywhere, so, for example, an output could get assigned to a pin you'd expect to be an input.
Marc
Check to see if the pin you lifted still appears shorted. There are some flux/cleaning/non-cleaning configurations that promote the growth of dendrites between PCB traces. Often a little mechanical action in the area of the microscopic short will open the short. If the lifted pin appears to work again, I'd look carefully at this.
It's not a signal near a battery on the board, is it? Those pesky voltages during assembly and cleaning are such a nuisance.
What nobody else has said, and you may or may not be familiar with, is "ESD", electrostatic discharge. The lower voltage devices are more and more sensitive to voltages generated by friction on common substances like clothing and plastic. You can generate thousands of Volts just sliding into a chair. If the pin shows shorted before the FPGA has been configured, it is most likely physical damage to the part. If it only shows the short after configuration, then it is a result of the FPGA configuration loaded into the part, and not physical in nature. If these pins became shorted just after you touched the board, or touched it with a tool or scope probe, suspect ESD. You can use commercial anti-ESD products like wrist straps, workstation pads, etc. or just use common sense plus awareness of these ESD problems to ground your body and your tools to a known grounded object like the case of a power supply, soldering iron handle or whatever you know is grounded before touching the board. Don't slide into a chair and grab the board first.
Jon
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