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AR# 7721

2.1i Ngdanno: Constants become hanging nets in back-annotated HDL file causing unknown states in timing simulation

Description

Keywords: ngdanno, ngm, back, annotated, back-annotated, power, ground, constants,
hanging, tied, off, unknown, timing, simulation

Urgency: Standard

General Description:

HDL design modules which have constants as inputs may output unknown values during
timing simulation. In the back-annotated simulation file, these inputs are hanging, hence the
simulation results unknown states. This is a result of ngdanno becoming confused when a
slice both generates and consumes a pwr/gnd signal.

Solution

Workaround is to preclude the .ngm file from being read by ngdanno. This can be accomplished
by deselecting 'Correlate Simulation Data to Input Design' under Simulation Options in Design
Manager.

AR# 7721
Date Created 09/21/1999
Last Updated 12/10/2001
Status Archive
Type General Article