Keyword: IOBUFDS, P TYPE, N TYPE
When I run a DRC check on my pin assignments, I receive errors on my bidirectional differential I/Os similar to the following:
"DDR_2_DQS_N<0> : Placement mismatch. Please check the following: 1. if this differential (sic) IO is placed in a differential IOB. 2. if it is placed in the same type (P or N TYPE) of differential IOB or if its a local clock IO, it is place in opposite type (P for N)"
Is this a valid error?
In some cases, PACE misinterprets the differential pairs. If you have verified that the location constraints are correct, you can ignore these errors.