Answers Database

XNFPREP: Error 3526: Illegally inverted pin with XBLOX SYNC_RAM symbol


Record #1051

Product Family:  Software

Product Line:  FPGA Core

Problem Title:
XNFPREP: Error 3526: Illegally inverted pin with XBLOX SYNC_RAM symbol


Problem Description:
During compilation of a XC4000E design containing an XBLOX SYNC_RAM
component, XNFPrep may give the following error:

   XNFPREP: ERROR 3526:
   The pin 'D' on the symbol <symbol name> (type = RAMS, output signal =
   [signal name]) is illegally inverted.  This pin in non-invertible.

This error is occurs while placing either an INVBUS symbol or INV symbol on
the WR_CLK pin to clock the synchronous RAM on the falling edge.  XBLOX
pushes the inversion onto the device pin instead of leaving the inverter
separate as it should.


Solution 1:

Place an X (explicit) property on the net between the INV/INVBUS and the
SYNC_RAM.  This will prevent the inverter from being absorbed into the D
pin of the synchronous RAM.



End of Record #1051