Flip Flops 4.1 Latches and Flip-Flops 4 ©Paul Godin Created September 2007 Last edit Sept 2009

Flip Flops 4.2 Input Types Flip-Flops have 2 types of inputs: ◊Synchronous ◊Waits for a clock input to change the state. ◊Asynchronous ◊Immediate change to the outputs without waiting for a clock pulse. Overrides the synchronous inputs.

Flip Flops 4.3 Examples of Asynchronous Inputs The preset and clear are asynchronous inputs. The J, K and Clock inputs are synchronous inputs.

Use of Asynchronous Inputs ◊Asynchronous inputs are used to force an immediate set or reset output to a single flip- flop or a group of flip-flops. ◊Active asynchronous outputs inhibit synchronous inputs. Flip Flops 4.4

Flip Flops 4.5 Asynchronous Immediate Synchronous On clock edge Remember

Flip Flops 4.6 JK ASYNCHRONOUS FLIP-FLOP

Flip Flops 4.7 D Flip Flop with asynch inputs ClkDPreClrQQ’Mode 01101Reset 11110Set 1X11QQ’Hold 0X11QQ’Hold X11QQ’Hold XX0110Preset XX1001Clear XX00??Invalid D Q Q Clock Preset Clear Synchronous Asynchronous Typically, active preset and clear generates a 1-1 output

Question ◊What often happens if the asynchronous inputs of a flip-flop are left floating? ◊Do asynchronous inputs need to be debounced? Flip Flops 4.8

Flip Flops 4.9 A few Flip-Flop circuits

Flip Flops 4.10 Explain how this device functions.

Flip Flops 4.11 An Asynchronous Debouncer Use this one in lab.

Flip Flops 4.12 Determine the output frequency if the input frequency is 1kHz:

Flip Flops 4.13 Sequence Detector Which input needs to be high first for a high Q output? (assume initial LOW inputs)

Flip Flops 4.14 Determine the input sequence to make Q 2 go high. Sequence Detector

Flip Flops 4.15 Challenge Determine the sequence of this circuit:

Flip Flops 4.16 Clock Pulse Switching Turn on/off a clocked output as required, without partial pulses or bounces.

Flip Flops 4.17 An unacceptable solution

Flip Flops 4.18 Solution using an edge-triggered D-Flip-Flop

Flip Flops 4.19 END © GMAIL.COM