R
XC5200 Series Field Programmable Gate Arrays
To GRM
M0-M23
24
8
TS
4
Global Nets
4
To
C
OUT
Longlines
and GRM
TQ0-TQ3
4
4
4
4
4
North
South
East
CLB
5
5
5
5
3
LC3
LC2
LC1
LC0
Input
Multiplexers
Output
Multiplexers
West
3
Direct to
East
V
CC
/GND
4
8
3
3
4
Direct North
4
CLK
CE
Feedback
4
CLR
C
IN
Direct West
4
4
X5724
Direct South
Figure 14: VersaBlock Details
CLB inputs have several possible sources: the 24 signals
from the GRM, 16 direct connections from neighboring
VersaBlocks, four signals from global, low-skew buffers,
and the four signals from the CLB output multiplexers.
Unlike the output multiplexers, the input multiplexers are
not fully populated; i.e., only a subset of the available sig-
nals can be connected to a given CLB input. The flexibility
of LUT input swapping and LUT mapping compensates for
this limitation. For example, if a 2-input NAND gate is
required, it can be mapped into any of the four LUTs, and
use any two of the four inputs to the LUT.
The direct connects also provide a high-speed path from
the edge CLBs to the VersaRing input/output buffers, and
thus reduce pin-to-pin set-up time, clock-to-out, and combi-
national propagation delay. Direct connects from the input
buffers to the CLB DI pin (direct flip-flop input) are only
available on the left and right edges of the device. CLB
look-up table inputs and combinatorial/registered outputs
have direct connects to input/output buffers on all four
sides.
The direct connects are ideal for developing customized
RPM cells. Using direct connects improves the macro per-
formance, and leaves the other routing channels intact for
improved routing. Direct connects can also route through a
CLB using one of the four cell-feedthrough paths.
Direct Connects
The unidirectional direct-connect segments are connected
to the logic input/output pins through the CLB input and out-
put multiplexer arrays, and thus bypass the general routing
matrix altogether. These lines increase the routing channel
utilization, while simultaneously reducing the delay
incurred in speed-critical connections.
General Routing Matrix
The General Routing Matrix, shown in Figure 15, provides
flexible bidirectional connections to the Local Interconnect
7-94
November 5, 1998 (Version 5.2)
ETC [ ETC ]
