Fast I/O registers in Bidirection IO

You have three settings at your disposal:

FAST_INPUT_REGISTER

FAST_OUTPUT_REGISTER

FAST_OUTPUT_ENABLE_REGISTER

For a bidirectional IO, you can set any or all of these to TRUE for the pin in question. Your design must of course actually support the function:

1 - The pin must be driven directly by a register output with no combinatorial logic.

2 - The input must be fed directly to a register with no combinatorial logic

3 - If you choose to use a fast output enable then the output enable for the pin must be driven directly by a register.

Jake

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For a bidirectional IO, you can set any or all of these to TRUE for the pin in question. Your design must of course actually support the function:

1 - The pin must be driven directly by a register output with no combinatorial logic.

2 - The input must be fed directly to a register with no combinatorial logic

3 - If you choose to use a fast output enable then the output enable for the pin must be driven directly by a register.

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Thank you for your rapidly reply!

When using a bidirection IO, the output and input are not directly fed by a register, but via a buffer.

Even if my output reg before bidirection buffer is register pipelined so that there is certainly no combinatorial logic. I think course 1 and 2 are not met because of the buffer itself.

Only the buffer's enable reg could be set in this condition?

thank you ag~

I should be more clear. Besides the buffer ... there can be nothing between the pin and register.

Jake

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I should be more clear. Besides the buffer ... there can be nothing between the pin and register.

Jake

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I think I've been thinking too much to waht you've said just now, hehe~

And so according to this, I just set and apply the Fast IO register constrains directly to the Bidir IO pin, it will do work.

Thank you very much!