Xilinx ISE Warning: FF/Latch <> is unconnected in block <>

Apr 21, 2005 2 Replies

Hi there,



I created a CPLD design which works perfect in simulation, but does not work in hardware. There are many warnings from the Xilinx ISE looking like



WARNING:Xst:1291 - FF/Latch is unconnected in block .



or



WARNING:Xst:1710 - FF/Latch (without init value) is constant in block .



These come up only in the Low Level Synthesis processing step. There is one relevant solution record on the Xilinx website (see

formatting link
with the following suggestion:


> When this warning occurs, a register or latch in your design has been

created, but the output is never connected or the signals or logic it drives have been trimmed. Check the XST log for messages such as the following to find signals that have been trimmed out of the design:


"WARNING:Xst:646 - Signal is assigned but never used."

formatting link

If working with ISE/Webpack 7.1, did you apply the the patch 21168?

formatting link

1&getPagePath=21168

Best regards Klaus

work

block

one

formatting link

drives

to

Thanks for your advice, I installed the newest ISE (7.1), service pack 1 and the patch. Now these strange warnings are gone.

Best regards Christian

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required