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Figure 31: basic 1-bit memory implemented on OR gate
The above 1- bit memory device operates as follows:
If A and Q are initially at zero (0), then output Q remains at zero (0). If A ever becomes a binary one (1),
then Q will be binary one (1) ever after, regardless any further changes in A. The operation of this 1-bit
memory can best be described by a state table or a time diagram.
Present State Input Next State
Qn A Qn + 1
0 0 0
0 1 1
1 1 1
1 0 1
1 1 1
Figure 32: 1-bit memory time diagram
The type of 1-bit memory describe above is a Read Only Memory (ROM), which is written once but
read many times. ROMs are programmed and inserted by the manufacturer.
12.2 The SR Latch
The SR latch is the simplest 1-bit memory (see logic circuit below)
Figure 33: SR 1-bit memory neither implemented on NOR gates
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