Designing Large Multiplexers - UG474

7 Series FPGAs Configurable Logic Block User Guide (UG474)

Document ID
UG474
Release Date
2025-04-01
Revision
1.9 English

4:1 Multiplexer

Each LUT can be configured into a 4:1 MUX. The 4:1 MUX can be implemented with a flip-flop in the same slice. Up to four 4:1 MUXes can be implemented in a slice, as shown in the following figure.

Figure 1. Four 4:1 Multiplexers in a Slice

8:1 Multiplexer

Each slice has an F7AMUX and an F7BMUX. These two MUXes combine the output of two LUTs to form a combinatorial function up to 13 inputs (or an 8:1 MUX). Up to two 8:1 MUXes can be implemented in a slice, as shown in the following figure.

Figure 2. Two 8:1 Multiplexers in a Slice

16:1 Multiplexer

Each slice has an F8MUX. F8MUX combines the outputs of F7AMUX and F7BMUX to form a combinatorial function up to 27 inputs (or a 16:1 MUX). Only one 16:1 MUX can be implemented in a slice, as shown in the following figure.

Figure 3. 16:1 Multiplexer in a Slice

It is possible to create multiplexers wider than 16:1 across more than one SLICEM. However, there are no direct connections between slices to form these wide multiplexers.