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AR# 2457

M1.2 MAP: Input flip-flops in a bidirectional I/O get removed due to optimization of an output flip-flop whose input is tied to GND.


Keywords: input flip-flops trim inff ifd ifdx ofd ofdtx ofdx

Urgency: standard

General Description:

Given a circuit consisting of a bidirectional I/O:

IOPAD connected to both the D input of an IFD and
the Q output of an OFDTX_F. The D input of the OFDTX_F is
connected to a constant value of "0" (GND) in the user's

Map simplifies the OFDTX_F to a constant value of 0, and the
IOPAD is correctly configured to drive a constant value of
ZERO in the output direction. However, the zero is
subsequently also pushed around to the D input of the IFD,
and this causes the IFD to be removed.


Attach a NOCLIP, KEEP, or S attribute to the affected pad net
(the 3 properties are equivalent) to prevent the pushing of the
zero to the input of the INFF.

This problem is fixed in the M1.3 release.

Reference No.: 17489
AR# 2457
Date Created 06/19/1997
Last Updated 10/07/1997
Status Archive
Type General Article