Answers Database

SYNOPSYS/XSI: Using an Input Latch (ILD_1) with No Delay


Record #174

Product Family:  Software

Product Line:  Synopsys

Problem Title:
SYNOPSYS/XSI: Using an Input Latch (ILD_1) with No Delay


Problem Description:
The  xc4000 input latch can be configured to have different delay options, using
 the
fast and nodelay properties. How are these attached in Synopsys?


Solution 1:

The standard input latch (ILD_1) available in the Xilinx-Synopsys interface libr
ary includes a built-in delay which  forces the input latch to have a zero hold
time.  This slows down the input latch.
In order to use an input latch without the built-in delay, Instantiate an ILD_1F
 primitive instead of an ILD_1 (INIT=Reset) or ILDI_1F instead of an ILDI_1 (INI
T=Set).

Note that these input latches without a built in delay must be instantiated as t
hey cannot
be automatically inferred.
See the Synopsys (XSI) for FPGAs Interface/Tutorial Guide, Appendix B, for more
details.




End of Record #174