Entering T-Specs in a UCF file

Entering Timespecs in a UCF file

You can create a UCF file with the same name as your design file, except with the .ucf extension. Then you can add timespecs to it using an editor. Then add a timespec property to the UCF file in the following format:

TIMESPEC TSnn=FROM:source_group:TO:destination_group:delay_value;

Source groups and destination groups consist of timing end-points which can be either pads (input, output or I/O pads) or flip-flops.

For example, the following timing constraint specifies that the maximum propagation delay from input pad IN1 to output pad OUT2 should be no more than 15 ns:

TIMESPEC TS02=FROM:PADS(IN1):TO:PADS(OUT2):15;

You can also use the Period timespec format to define the maximum period of any clock:

TIMESPEC TSnn=PERIOD:clock_group:period_value;

For example:

TIMESPEC TS01=PERIOD:CLK_GRP:15;

To define a timing group name that you can use as the source group or destination group in a timespec, you can either use the TNM property or specify a timegroup definition using the TIMEGRP property.

To use TNM, apply a property to a pad or flip-flip instance (or registered macro) in your design via the UCF file using the following format:

INST instance_name TNM=group_name;

To specify a timegroup definition, specify a timegroup property in the UCF file using the following format:

TIMEGRP new_group_name=group_name[:group_name]...;

For details on how to form group names using TNM and timegroup definitions, see Grouping Signals.

Note: The TIG (Timing IGnore) attribute and the TIG timespec keyword are currently not supported for CPLD designs. The RAMS, LATCHES, TPTHRU and TPSYNC timespec keywords are also not used for CPLD designs.

If you want to temporarily ignore all timing constraints in your design when you run the fitter, turn off the Use Timing Constraints option in the Basic tab of Process Properties of the Project Navigator, or, in the Design Manager at the Basic tab of the Implementation Options template. This can be useful if you want to try your design in a different target device or speed grade.

See Also