MA Mingyu (Derek) | Nov 12, 2017
derek.ma | derek.ma@connect.polyu.hk
Characteristic table:
\(S\) | \(R\) | \(Q(t)\) | \(Q(t+\Delta)\) |
---|---|---|---|
0 | 0 | 0 | disallowed |
0 | 0 | 1 | disallowed |
0 | 1 | 0 | 1 |
0 | 1 | 1 | 1 |
1 | 0 | 0 | 0 |
1 | 0 | 1 | 0 |
1 | 1 | 0 | 0 |
1 | 1 | 1 | 1 |
K-map:
row:\(SR\); col:\(Q(t)\) | 00 | 01 | 11 | 10 |
---|---|---|---|---|
0 | X | 1 | 0 | 0 |
1 | X | 1 | 1 | 0 |
Next-state equation:
\(Q(t+\Delta) = \overline{S(t)} + R(t)Q(t)\)
The relationship between this latch and the one using NOR gates is exact opposite.
\(S\) here is actually \(\overline{S}\), and \(R\) here is actually \(\overline{R}\) compared to the one using NOR gates.
Characteristic table for this latch:
\(E\) | \(D\) | \(Q\) | \(Q_{next}\) | \(\overline{Q_{next}}\) |
---|---|---|---|---|
0 | X | 0 | 0 | 1 |
0 | X | 1 | 1 | 0 |
1 | 0 | X | 0 | 1 |
1 | 1 | X | 1 | 0 |
where X means "don't care the value of this variable".
Another possible characteristic table is:
\(E\) | \(D\) | \(Q\) | \(Q_{next}\) | \(\overline{Q_{next}}\) |
---|---|---|---|---|
0 | 0 | X | \(Q\) | \(\overline{Q}\) |
0 | 1 | X | \(Q\) | \(\overline{Q}\) |
1 | 0 | X | 0 | 1 |
1 | 1 | X | 1 | 0 |