Controlling Design Implementation
CPLD Schematic Design Guide
3-19
1.
In the Clock to Pad column and in the row associated with the
appropriate port name, double-click the left mouse button. This
opens the Clock to Pad dialog box.
Note:
An alternate way to invoke the Clock to Pad dialog box: right
click in any row or column (except the heading), then click
Clock
to Pad
from the pop-up window.
2.
Enter a time requirement in the Time Requirement text box and
the desired unit from the pull-down list.
3.
Select the clock that clocks this input from the Relative to Clock
Net pull-down list.
4.
Click
OK
.
Slow/Fast Path Exceptions (FROM/THRU/TO)
This generates the FROM/THRU/TO dialog box, which allows you
to specify an explicit maximum delay between groups of elements
and through intermediate points.
This is particularly useful for defining pad-to-pad propagation delays
between specific device pins.
1.
Click
Specify
in the Slow/Fast Path Exceptions (FROM/
THRU/TO) field. This opens the FROM/THRU/TO dialog box.
2.
In the Time Spec text box enter a time specification name. The
name should be entered in the form TSid, where id is a unique
name. The name can consist of letters, numbers, or the under-
score character (_). If you do not enter TS, the software will auto-
matically place it before your id
3.
Make a selection from the From Group and To Group pull-down
lists (All, All FFS, All PADS).
4.
Enter a value for time in the Time text box and select the appro-
priate unit from the Units pull-down list.
·
Click
OK
.
Entering Timing Specifications in a Schematic
The TIMESPEC schematic primitive, as illustrated in the "TIMESPEC
Primitive" figure, serves as a placeholder for timing specifications,
which are called TS attribute definitions. Every TS attribute must be