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sth125's avatar
sth125
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2 years ago
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Warning (13028): Removed fan-out from the always-disabled I/O buffer....

Hello, I am getting the following warnings related to two 74541 Octal Buffers (See image below): Warning (13027): Removed fan-outs from the following always-disabled I/O buffers Warning (13028): R...
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  • sstrell's avatar
    sstrell
    2 years ago

    So what is the issue and your goal at this point? You have disabled tri-state buffers that are not being used in the design.

    Also, it should be mentioned that there is no tri-state logic internal to the FPGA fabric, only in the I/O cells, so that may be part of the issue here as well. Note "I/O buffer" in the warning.

    If you are trying to determine what resources are being used and what has been removed, use the Technology Map Viewer (Post-fitting) to see a schematic of the used device resources post-fit.

sth125's avatar
sth125
Icon for New Contributor rankNew Contributor
2 years ago

If DI_INT_CS4_ is always logic high, the output of the NAND gate will always be high no matter what the logic state of the other input is. Therefore, I wouldn't think the other input would matter.

Also, the built-in help says the following about the warning:

ID:13027 Removed fan-outs from the following always-disabled I/O buffers

CAUSE: The design contains one or more tri-state buffers that have their output-enable input tied to GND. These tri-state buffers will never provide any useful data to the pins/nodes they feed.As a result, the Quartus Prime software has removed this fan-in. For example, the following Verilog design gives this warning for the tri-state node triwire:
For my situation, I tied DI_INT_CS4_ to Vcc, which means the output enables are always logic high.