surrounding one CLB in the array. Each Switch Matrix
consists of programmable n-channel pass transistors used
to establish connections between the single-length lines
(Figure 7). For example, a signal entering on the right side
of the Switch Matrix can be routed to a single-length line on
the top, left, or bottom sides, or any combination thereof,
if multiple branches are required. Single-length lines are
normally used to conduct signals within a localized area
and to provide the branching for nets with fanout greater
than one.
Compared to the previous generations of LCA archi-
tectures, the number of possible connections through the
Switch Matrix has been reduced. This decreases capaci-
tive loading and minimizes routing delays, thus increasing
performance. However, a much more versatile set of
connections between the single-length lines and the CLB
inputs and outputs more than compensate for the reduc-
tion in Switch Matrix options, resulting in overall increased
routability.
The function generator and control inputs to the CLB (F1-
F4, G1-G4, and C1-C4) can be driven from any adjacent
single-length line segment (Figure 6). The CLB clock (K)
input can be driven from one-half of the adjacent single-
length lines. Each CLB output can drive several of the
single-length lines, with connections to both the horizontal
and vertical Longlines.
The double-length lines (Figure 8) consist of a grid of metal
segments twice as long as the single-length lines; i.e, a
double-length line runs past two CLBs before entering a
Switch Matrix. Double-length lines are grouped in pairs
with the Switch Matrices staggered so that each line goes
through a Switch Matrix at every other CLB location in that
row or column. As with single-length lines, all the CLB
inputs except K can be driven from any adjacent double-
length line, and each CLB output can drive nearby double-
length lines in both the vertical and horizontal planes.
Double-length lines provide the most efficient imple-
mentation of intermediate length, point-to-point inter-
connections.
CLB
CLB
CLB
CLB
Switch
Matrices
X3245
Figure 8. Double-Length Lines
Longlines form a grid of metal interconnect segments that
run the entire length or width of the array (Figure 9).
Additional vertical longlines can be driven by special global
buffers, designed to distribute clocks and other high fanout
control signals throughout the array with minimal skew.
Longlines are intended for high fan-out, time-critical signal
nets. Each Longline has a programmable splitter switch at
its center, that can separate the line into two independent
routing channels, each running half the width or height of
the array. CLB inputs can be driven from a subset of the
adjacent Longlines; CLB outputs are routed to the Lon-
glines via 3-state buffers or the single-length intercon-
nected lines.
F4
G1
C1
K
F1
X
XQ
C4
G4
YQ
Y
G3
CLB
C3
F3
F2
C2
G2
Six Pass Transistors
Per Switch Matrix
Interconnect Point
X3244
“Global”
Long Lines
“Global”
Long Lines
X5520
Figure 7. Switch Matrix
Figure 9. Longline Routing Resources with
Typical CLB Connections
2-15
XILINX [ XILINX, INC ]
