### Logic Experiment 8

```Rise and rise again until lambs become lions

Rise and rise again until lambs become lions
Outlines
Sequential logic circuits
– Memory and Clock
SR latch
D Flip-Flop
Lab
Rise and rise again until lambs become lions
Sequential logic circuits
Combinational logic circuits
– depends only on current inputs
Sequential logic circuits
– depends on past and current inputs
Memory and Clock!!
Rise and rise again until lambs become lions
SR Latch
SR Latch (Memory)
0R
Q 1
1 S
Q’ 0
1R
Q0
0 S
Q’ 1
1R
QQ
1S
Q’ Q’
R
Q
Q’
S
Input
Function
S = 1，R = 0
Set ( Q 設為 1 )
S = 0，R = 1
Reset ( Q 設為 0 )
S = 1，R = 1
Hold ( Q 保持不變 )
S = 0，R = 0

Rise and rise again until lambs become lions
Clock
When to set and reset
How to synchronize devices with memory
time
– Positive (rising) edge triggered
– Negative (falling) edge triggered
Rise and rise again until lambs become lions
Flip Flops
Input type
– SR、D、JK、T
Trigger type
– Rising(positive)-edge
– Falling(negative)-edge
Rise and rise again until lambs become lions
D-type positive edge triggered FF
1
2
R
5
Clock
SR Latch
3
D
Q
4
6
S
Q’
Rise and rise again until lambs become lions
D Flip Flop
Clock = 0
Clock: 0->1
X
X
X->X
R
R
R
1
1
X’
XD
Clock
Clock
S, R will not change with D
1
X
S
S
XD
X’
1->X’
S = X, R = X’
X
0->1⟹ Set the latchas1->X
ClockS, R = 1 ⟹ Hold
0
Clock = 1, D: X->X’
X’
S
D
X->X’
X’->1
Rise and rise again until lambs become lions
Lab
Today’s target: D-type positive edge triggered Flip-Flop
IC： 7400 (NAND) x 2、LED x 1
3
How to realize three-inputs NANDs
with two-inputs NANDs?
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