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Altera_Forum
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11 years ago

Cyclone III EP3C25 - Pin 141 can't drive signal ?

Hello everybody

I have a problem with a Cyclone III EP3C25E144I7N FPGA.

I try to affect an output (UART_TX) to the pin 141.

Observing it with a scope, the output stays at 1.

When I change the pin, for the pin 144 for example, the output is the expected one (UART data).

I look the ep3c25 pin information (http://www.altera.com/literature/dp/cyclone3/ep3c25.pdf) to check if the pin 141 was a specific pin (pll, clk, vdd ?) : it seems to be not the case.

Is there a non-documented defect or specific usage with the pin 141 ?

Regards

--

bploujoux

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    11 years ago

    Have you tried driving some other signal out of this pin - such as the result of a simple register toggling every clock cycle or the clock itself?

    You don't say what package you're using. However, assuming pin 141 is a standard I/O pin then it should behave as pin 144. Check that it isn't a pin with a reserved function or a dedicated clock input. Compilation should fail if you've incorrectly constrained it to such a pin, but worth checking.

    A quick look at the packages shows pin 141 is perfectly valid if you're using an E144 package. However, it's a GND connection in the Q240 package - invalid. Again compilation should fail if you specify this.

    Cheers,

    Alex

    Ammendment:

    PS. I subsequently see you did specify the package you're using... :) So, it should all work as you expect.
  • Altera_Forum's avatar
    Altera_Forum
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    11 years ago

    Thanks for your response, Alex.

    To sum up, I've cleared the following hypothesis :

    - fault in VHDL : with a simple design that stuck the output at 0

    - fault on the circuit / external pull-up : tried to disconnect fpga from the rest of the circuit

    - fault on FPGA component itself : I have two different wired boards, the probability to have the fault on two FPGA is low

    In ALL of these cases, the output remains at 1.

    I'm right now investigating a PCB defect..

    Edit

    --

    The last hypothesis was the good one : I found a short circuit in PCB routing.

    Solution : isolate the short circuit, replace the isolated track with a simple wire.

    Thread is closed !