notes/education/computer engineering/ECE2700/Sequential Circuits.md

• Output depends on input and past behavior
• Requires use of storage elements

Latches

SR Latch

SR stands for Set/Reset, and functions like so:

• When a signal comes into S, Q_a is set on and stays on until a signal comes into R, at which point the output (Q_a) is reset, back to zero.
• S and R are interchangeable, it just impacts whether Q_a or Q_b is set/reset. Truth table:

S	R	Q_a	Q_b
0	0	0/1	1/0
0	1	0	1
1	0	1	0
1	1	0	0
!

Gated Latch

A gated latch is similar to a basic latch, but the output only changes when clk = 1.

D Latch

A D latch has two inputs, clk and data. When clk is high, data is stored.

Flip Flops

A latch, but the output only changes on one of the clock edges

• Can be a rising edge latch or a falling edge latch

JK Flip Flop

Similar to an SR flip flop, a JK flip flop has set/reset inputs, but when both inputs are high, then the output is toggled.

T Flip Flop

A T Flip Flip, or a toggle flip flop has two inputs:

• clk - Clock input
• T - Whenever T goes from low to high, the output toggles its state

Registers

Shift Register

! Above is a simple shift register.

Parallel Shift Register

A parallel shift register has 4 inputs, 4 outputs, a serial input, and a shift/load input.

When the load input is high, the input is stored into the register. When the shift input is high, the registers are shifted and the serial input is read into the new space.

Counters

A 3-bit Up-counter

!

Synchronous Sequential Circuits

• A synchronous circuit is clock driven, while an asynchronous circuit is not.