AN921 Datasheet, PDF (3/24 Pages) Silicon Laboratories – Configurable Logic Unit

AN921: Configurable Logic Unit
SR Latch
2. SR Latch
Configurable Logic Units can be used to build a SR latch. This section shows how this memory circuit can be built without using the D
flip-flop portion of the CLU. This is advantageous in applications where we may want the output of the latch to be sent to another CLU
via the carry input.
2.1 Background
The truth table for an SR latch is shown below. When the inputs SET = RESET = 0, the next output (Q_NEXT) will remain the same as the
current output (Q). When SET = 0, RESET = 1, the next output will be reset to 0. When SET = 1, RESET = 0, the next output will be set
to 1. When SET = RESET = 1, the next output is not defined.
Table 2.1. Truth Table of SR Latch (Simplified)
SET
RESET
Q
0
0
X
0
1
X
1
0
X
1
1
X
Q_NEXT
Q
0
1
Undefined
Comments
Hold state
Reset
Set
Undefined
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