Xilinx virtex-5 fpga

234 www.xilinx.com Virtex-5 FPGA User Guide
UG190 (v5.0) June 19, 2009
Chapter 6: SelectIO Resources
OBUFT
The generic 3-state output buffer OBUFT, shown in Figure 6-20, typically implements
3-state outputs or bidirectional I/O.
IOBUF
The IOBUF primitive is needed when bidirectional signals require both an input buffer and
a 3-state output buffer with an active High 3-state pin. Figure 6-21 shows a generic Virtex-5
FPGA IOBUF.
IBUFDS and IBUFGDS
The usage and rules corresponding to the differential primitives are similar to the single-
ended SelectIO primitives. Differential SelectIO primitives have two pins to and from the
device pads to show the P and N channel pins in a differential pair. N channel pins have a
“B” suffix.
Figure 6-22 shows the differential input buffer primitive
X-Ref Target - Figure 6-20
Figure 6-20: 3-State Output Buffer (OBUFT) Primitive
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OBUFT
O (Output)
to device pad
I (Input)
From FPGA
T
3-state input
X-Ref Target - Figure 6-21
Figure 6-21: Input/Output Buffer (IOBUF) Primitive
ug190_6_19_022806
IOBUF
I/O
to/from device pad
I (Input)
from FPGA
O (Output)
to FPGA
T
3-state input
X-Ref Target - Figure 6-22
Figure 6-22: Differential Input Buffer Primitive (IBUFDS/IBUFGDS)
ug190_6_20_022806
+
–
I
IB
O
IBUFDS/IBUFGDS
Inputs from
device pads
Output to
FPGA