R
Spartan and Spartan-XL Families Field Programmable Gate Arrays
4-10
DS060 (v1.5) March 2, 2000
CLB Routing Channels
The routing channels around the CLB are derived from
three types of interconnects; single-length, double-length,
and longlines. At the intersection of each vertical and hori-
zontal routing channel is a signal steering matrix called a
Programmable Switch Matrix (PSM).
Figure 8
shows the
basic routing channel configuration showing single-length
lines, double-length lines and longlines as well as the CLBs
and PSMs. The CLB to routing channel interface is shown
as well as how the PSMs interface at the channel intersec-
tions.
CLB Interface
A block diagram of the CLB interface signals is shown in
Figure 9
. The input signals to the CLB are distributed
evenly on all four sides providing maximum routing flexibil-
ity. In general, the entire architecture is symmetrical and
regular. It is well suited to established placement and rout-
ing algorithms. Inputs, outputs, and function generators can
freely swap positions within a CLB to avoid routing conges-
tion during the placement and routing operation. The
exceptions are the clock (K) input and CIN/COUT signals.
The K input is routed to dedicated global vertical lines as
well as four single-length lines and is on the left side of the
CLB. The CIN/COUT signals are routed through dedicated
interconnects which do not interfere with the general rout-
ing structure. The output signals from the CLB are available
to drive both vertical and horizontal channels.
Programmable Switch Matrices
The horizontal and vertical single- and double-length lines
intersect at a box called a programmable switch matrix
(PSM). Each PSM consists of programmable pass transis-
tors used to establish connections between the lines (see
Figure 10
For example, a single-length 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. Similarly, a dou-
ble-length signal can be routed to a double-length line on
any or all of the other three edges of the programmable
switch matrix.
Single-Length Lines
Single-length lines provide the greatest interconnect flexi-
bility and offer fast routing between adjacent blocks. There
are eight vertical and eight horizontal single-length lines
associated with each CLB. These lines connect the switch-
ing matrices that are located in every row and column of
CLBs.
Figure 9: CLB Interconnect Signals
Rev 1.1
CLB
F
F3
G3
C3
Y
Y
C
C1
G1
F1
X
CIN
G
F
X
C
K
G
COUT
Figure 10: Programmable Switch Matrix
Six Pass Transistors Per
Switch Matrix Interconnect Point
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