Spartan-3E FPGA Family: Functional Description
X-Ref Target - Figure 18
Wide Multiplexers
Y
For additional information, refer to the “Using Dedicated
Multiplexers” chapter in UG331.
4
D
YQ
G[4:1]
A[4:1]
G-LUT
FFY
FFX
Wide-function multiplexers effectively combine LUTs in
order to permit more complex logic operations. Each slice
has two of these multiplexers with F5MUX in the bottom
portion of the slice and FiMUX in the top portion. The
F5MUX multiplexes the two LUTs in a slice. The FiMUX
multiplexes two CLB inputs which connect directly to the
F5MUX and FiMUX results from the same slice or from
other slices. See Figure 19.
X
4
F[4:1]
A[4:1]
F-LUT
XQ
D
DS312-2_33_111105
Figure 18: LUT Resources in a Slice
X-Ref Target - Figure 19
FiMUX
FXINA
1
0
FX (Local Feedback to FXIN)
Y (General Interconnect)
YQ
FXINB
BY
D Q
F5MUX
1
LUT
LUT
F[4:1]
G[4:1]
BX
F5 (Local Feedback to FXIN)
X (General Interconnect)
XQ
0
D Q
x312-2_34_021205
Figure 19: Dedicated Multiplexers in Spartan-3E CLB
Depending on the slice, FiMUX takes on the name F6MUX,
F7MUX, or F8MUX. The designation indicates the number
of inputs possible without restriction on the function. For
example, an F7MUX can generate any function of seven
inputs. Figure 20 shows the names of the multiplexers in
each position in the Spartan-3E CLB. The figure also
includes the direct connections within the CLB, along with
the F7MUX connection to the CLB below.
Each mux can create logic functions of more inputs than
indicated by its name. The F5MUX, for example, can
generate any function of five inputs, with four inputs
duplicated to two LUTs and the fifth input controlling the
mux. Because each LUT can implement independent 2:1
muxes, the F5MUX can combine them to create a 4:1 mux,
which is a six-input function. If the two LUTs have
completely independent sets of inputs, some functions of all
nine inputs can be implemented. Table 11 shows the
connections for each multiplexer and the number of inputs
possible for different types of functions.
DS312 (v4.2) December 14, 2018
www.xilinx.com
Product Specification
26
XILINX [ XILINX, INC ]
