Xilinx Constraints Guide

Chapter 4: Xilinx Constraints
Schematic LOC=SLICE_XlY5
UCF INST “/top-12/fdrd” LOC=SLICE_X1Y5;
Example Two
Place the flip-flop in the rectangular area bounded by the SLICE_X1Y1 in the lower left
corner and SLICE_X5Y7 in the upper right corner.
Schematic LOC=SLICE_R1C1:SLICE_R5C7
UCF INST “/top-12/fdrd”
LOC=SLICE_X1Y1:SLICE_X5Y7;
Example Three
Place the flip-flops anywhere in the row of slices whose Y coordinate is 3. Use the
wildcard (*) character in place of either the X or Y value to specify an entire row (Y*)
or column (X*) of slices.
Schematic LOC=SLICE_X*Y3
UCF INST “/top-12/fdrd/top-54/fdsd”
LOC=SLICE_X*Y3;
Example Four
Place the flip-flop in either SLICE_X2Y4 or SLICE_X7Y9.
Schematic LOC=SLICE_X2Y4,SLICE_X7Y9
UCF INST “/top-54/fdsd” LOC=SLICE_X2Y4,
SLICE_X7Y9;
In Example Four, repeating the LOC constraint and separating each such constraint by a
comma specifies multiple locations for an element. When you specify multiple locations,
PAR can use any of the specified locations.
Example Five
Do not place the flip-flop in the column of slices whose X coordinate is 5. Use the
wildcard (*) character in place of either the X or Y value to specify an entire row (Y*)
or column (X*) of slices.
Schematic PROHIBIT=SLICE_X5Y*
UCF CONFIG PROHIBIT=SLICE_X5Y*;
I/O Constraint Examples
You can constrain I/Os to a specific IOB. You can assign I/O constraints from the
schematic or through the UCF file.
From the schematic, attach LOC constraints to the target PAD symbol. The constraints
are then passed into the netlist file and read by PAR after mapping.
Alternatively, in the UCF file a pad is identified by a unique instance name. The
following example shows how the LOC constraint is applied to a schematic and to
a UCF (User Constraints File). In the examples, the instance names of the I/Os are
/top-102/data0_pad and /top-117/q13_pad. The example uses a pin number to lock to
one pin.
Constraints Guide
164 www.xilinx.com UG625 (v. 13.2) July 6, 2011