Verilog

EE271 @ Thuy T. Le

SJSU - EE

EE271
Advanced Digital System Design & Synthesis

Short Review of Sequential Circuits
Let’s take 3 lectures to review this topic

Appendix 2: Short Review of Sequential Circuits

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Overview
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Sequential circuits – state value at a given time depend on the history of the applied inputs and the current inputs The history of the inputs is represented by the state of the circuit – requires storage to store the state of the circuit. All sequential circuits require feedback: Next state of the circuit to be determined from the present state and inputs. The number of states of a sequential circuit is finite and (so call Finite State Machine) Sequential circuits can be asynchronous or synchronous (clocked).

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Appendix 2: Short Review of Sequential Circuits

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Appendix 2: Short Review of Sequential Circuits

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EE271 @ Thuy T. Le

SJSU - EE

Concepts of the State Machine
Computer Hardware = Datapath + Control Control • FSM generating sequences of control signals • Instructs datapath what to do next
Data inputs
State

Control signal outputs

Datapath • Storages • Combinational Functional Units (e.g., ALU) • Busses
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Basic Storage Components
Components: CMOS

Appendix 2: Short Review of Sequential Circuits

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Appendix 2: Short Review of Sequential Circuits

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EE271 @ Thuy T. Le

SJSU - EE

Switch and NOR

Appendix 2: Short Review of Sequential Circuits

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Storage elements may be clocked or unclocked. Can be level-sensitive called latches (unclocked) or edgesensitive called flip-flops (clocked)
R Q R' Q'

R-S Latch (unclocked)
S Q' S' Q

S 0 0 1 1

R 0 1 0 1

Q next Q 0 1 0

Q' next Q' 1 0 0
Hold Reset Set Not Allowed

S' 0 0 1 1

R' 0 1 0 1

Q next 1 1 0 Q

Q' next 1 0 1 Q'
Not Allowed Set Reset Hold

Appendix 2: Short Review of Sequential Circuits

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