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Altera_Forum
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11 years ago

I/O Pins show 1.12V on scope

I have a small custom board that is just a fanout of the I/O pins and PLL and dedicated Clock pins using a EP3C40 (Quad Plastic 240 pin pack) FPGA. I have scoped out several I/O and dedicated CLK pin...
Altera_Forum's avatar
Altera_Forum
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11 years ago

When you say you see a DC voltage of 1.12V, I assume that you mean you see only a DC voltage, and no switching AC signal on top of that. If so, here are some things you might consider:

1. Double-check your assignments. Have you assigned the correct signal to the correct pin, assigned it as an output, and selected the correct output standard?

2. Simulate the circuit. Does the simulator show the expected signal on that pin?

3. If the above are all OK, think about the bandwidths of your device and your oscilloscope. I recently saw a similar DC level when I inadvertently drove a 1 GHz PLL output signal to a 2.5V CMOS output. If your signal exceeds the bandwidth capability of the output pin/IO standard or the bandwidth of your scope, you could see a mid-signal DC level.