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3.1i WebPACK XST - "ERROR: NGDBuild:467 - output pad net '' has an illegal buffer"
Keywords: WebPACK, OBUFT, OBUF, tri, 3-state, web, pack, NGDBuild, NGD, build, buffer
When using an OBUFT in a schematic design in WebPACK for an XC9500 device, I encounter the following "NGDBuild:467" error:
ERROR: NGDBuild:467 - output pad net '' has an illegal buffer.
This has been fixed in WebPACK 4.1i.
Work-around for WebPACK 3.1i:
The bug prevents XST from realizing that the OBUFT is an output buffer; therefore, XST places an OBUF after the OBUFT. This is an illegal connection, which generates the error in NGDBuild.
The work-around is to use the OBUFE with an inverter on the enable line; this provides logic that is equivalent to an OBUFT. XST properly recognizes the OBUFE as an output buffer.