XC3S50 Datasheet, PDF (38/192 Pages) Xilinx, Inc – Revolutionary 90-nanometer process technology

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Spartan-3 1.2V FPGA Family: Functional Description
Interconnect
Interconnect (or routing) passes signals among the various
functional elements of Spartan-3 devices. There are four
kinds of interconnect: Long lines, Hex lines, Double lines,
and Direct lines.
Long lines connect to one out of every six CLBs (see
Figure 19a). Because of their low capacitance, these lines
are well-suited for carrying high-frequency signals with min-
imal loading effects (e.g. skew). If all eight Global Clock
Inputs are already committed and there remain additional
clock signals to be assigned, Long lines serve as a good
alternative.
Hex lines connect one out of every three CLBs (see
Figure 19b). These lines fall between Long lines and Dou-
ble lines in terms of capability: Hex lines approach the
high-frequency characteristics of Long lines at the same
time, offering greater connectivity.
Double lines connect to every other CLB (see Figure 19c).
Compared to the types of lines already discussed, Double
lines provide a higher degree of flexibility when making con-
nections.
Direct lines afford any CLB direct access to neighboring
CLBs (see Figure 19d). These lines are most often used to
conduct a signal from a "source" CLB to a Double, Hex, or
Long line and then from the longer interconnect back to a
Direct line accessing a "destination" CLB.
CLB
CLB
CLB
CLB
CLB
CLB
CLB
CLB
CLB
CLB
6
6
6
6
6
(a) Long Line
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8
CLB
CLB
CLB
CLB
CLB
(b) Hex Line
CLB
CLB
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2
CLB
CLB
CLB
CLB
CLB
CLB
CLB
CLB
CLB
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(c) Double Line
CLB
CLB
CLB
Figure 19: Types of Interconnect
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(d) Direct Lines
DS099-2 (v1.2) July 11, 2003
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