XC3S5000-5FGG676C Datasheet, PDF (45/272 Pages) Xilinx, Inc – Introduction and Ordering Information

Spartan-3 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 section [a] of Figure 25). Because of their low capacitance, these lines
are well-suited for carrying high-frequency signals with minimal 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 section [b] of Figure 25). These lines fall between Long lines and Double
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 section [c] of Figure 25). Compared to the types of lines already discussed,
Double lines provide a higher degree of flexibility when making connections.
Direct lines afford any CLB direct access to neighboring CLBs (see section [d] of Figure 25). 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.
For more details, refer to the “Using Interconnect” chapter in UG331.
X-Ref Target - Figure 25
CLB
CLB
CLB
CLB
CLB
CLB
CLB
CLB
CLB
CLB
6
6
6
6
(a) Long Lines
8
6
DS099-2_19_040103
CLB
CLB
CLB
CLB
CLB
(b) Hex Lines
CLB
CLB
DS099-2_20_040103
2
CLB
CLB
CLB
CLB
CLB
CLB
CLB
CLB
CLB
DS099-2_21_040103
(c) Double Lines
CLB
CLB
CLB
Figure 25: Types of Interconnect
DS099-2_22_040103
(d) Direct Lines
DS099 (v3.1) June 27, 2013
www.xilinx.com
Product Specification
45