Master-slave - D-Flip-flop Negative edge triggered Positive edge triggered D Flip-flop Preset and Clear Implementation Circuits using D Flip-flop Data latches Detecting the sequence of Edges

1. Digital Design – © 2020 Mouli Sankaran Email: mouli.sankaran@yahoo.com

2. Digital Design – © 2020 Mouli Sankaran Email: mouli.sankaran@yahoo.com 2
Session 20: Focus
 Master-slave - D-Flip-flop
◦ Negative edge triggered
◦ Positive edge triggered
 D Flip-flop
◦ Preset and Clear Implementation
 Circuits using D Flip-flop
◦ Data latches
◦ Detecting the sequence of Edges

3. Digital Design – © 2020 Mouli Sankaran Email: mouli.sankaran@yahoo.com
Master-Slave D Flip-flop
Negative and Positive Triggered

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Master-Slave D-Flip-flops
Positive edge Triggered D Flip-flop
Q
Negative edge Triggered D Flip-flop
Q

5. Digital Design – © 2020 Mouli Sankaran Email: mouli.sankaran@yahoo.com
D Flip-flop
Preset and Clear

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Preset and Clear Signals: D Flip-Flop
 Preset and Clear are Active low signals, force Q to 1 and 0
6
Clear
Preset
Positive edge
triggered
D Flip-flop
Direct Set (S): Preset
Direct Reset (R): Clear
Function Table

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Preset and Clear Signals: D Flip-Flop
 Preset and Clear are asynchronous signals which force Q to
one and zero
 They are independent of the other synchronous input signals
D and CLK
 Useful to force or initialize the flip-flops with either 0 or 1
D
D
NC: No Change

8. Digital Design – © 2020 Mouli Sankaran Email: mouli.sankaran@yahoo.com
Circuits using D-Flip-flops

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Example 1: 4-bit Data Latch
 A data latch can be used as a device to hold or remember the
data present on its data input
◦ Thereby each D-Flip-flop acts like a single bit memory device

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Example 2: Detecting the Sequence of Edges
 Here, D flip-flop is used to detect whether a positive-
going edge A follows or precedes another positive-
going edge B.
 If A happens before B:
 If A happens after B:
10
Signal
Given to D
Signal
Given to CLK
Positive edge triggered D Flip-flop
Q goes from Zero to One at B
Q remains at Zero
Initially Q is Zero

11. Digital Design – © 2020 Mouli Sankaran Email: mouli.sankaran@yahoo.com 11
Session 20: Summary
 Master-slave - D-Flip-flop
◦ Negative edge triggered
◦ Positive edge triggered
 D Flip-flop
◦ Preset and Clear Implementation
 Circuits using D Flip-flop
◦ Data latches
◦ Detecting the sequence of Edges

12. Digital Design – © 2020 Mouli Sankaran Email: mouli.sankaran@yahoo.com 12
References
Ref 1 Ref 2