ELCT 501: Digital System Design - German …eee.guc.edu.eg/Courses/Electronics/ELCT501 Digital System...Elements used in ASM Charts Dr. Mohamed Abd el Ghany 3 Department of Electronics

ELCT 501:

Digital System Design

Lecture 8: System Design

Dr. Mohamed Abd El Ghany,

Department of Electronics and Electrical Engineering

Algorithmic State Machine (ASM)

2Dr. Mohamed Abd el Ghany


ELCT 501: Digital System

Design

For large machines, the designers often use

a different form of representation, called the

algorithmic state machine chart.

An ASM chart is a type of flowchart that can

be used to represent the state transitions

and generated outputs for an FSM.

Elements used in ASM Charts




Design

Output

signals or

actions

(Moore type)

Condition

expression

Conditional outputs or

actions (Mealy type)

State name

0 (false) 1 (true)

State box Decision box

Conditional output box

From FSM to ASM chart




Design

A

Reset

w0

1B

w0

1

Z

C

w0 1

From FSM to ASM chart




Design

A

Reset

w0

1B

w0 1

z

Design Example




Design

Design A Bit-Counting Circuit to count the

number of bits in a register

B = 0;

While A ≠ 0 do

if a0 = 1 then

B= B+1;

end if;

Right-shift A;

End while;

Pseudo-

code for

the bit

counter

ASM chart for the

pseudo-code




Design

B = 0;

While A ≠ 0 do

if a0 = 1 then

B= B+1;

end if;

Right-shift A;

End while;

B <- 0

S1

Reset

s0

1

S2

A=0?

0

1

Shift right A

Load A

a00

B<-B+1

Done

s

1

1

0

S3

Datapath for the ASM chart




Design

Shift register

Data

Counter

Clock

L

E

w

L

E

0

log2nn

log2n

LB

EB

0

LA

EA

A

n

B

a0z

ASM chart for the

control circuit




Design

LB

S1

Reset

s0

1

S2

z

0

1

EA

a00

EB

Done

s

1

1

0

S3

VHDL for the bit-

counting circuit




Design

Part 1

VHDL for the bit-

counting circuit




Design

Part 2

VHDL for the bit-

counting circuit




Design

Part 3

VHDL for the bit-

counting circuit




Design

Part 4

Design Example




Design

Design a shift-and-add multiplier

Decimal

13

x 11

-----------

13

13

-----------

143Manual

method

Binary

1101

x 1011

--------------

1101

1101

0000

1101

---------------

10001111

Design Example




Design

Design a shift-and-add multiplier

P = 0;

For i =0 to n-1 do

if bi = 1 then

P= P+A;

end if;

Left-shift A;

End For;

Pseudo-

code

Binary

1101

x 1011

--------------

1101

1101

0000

1101

---------------

10001111

ASM chart for the

multiplier




Design

P <- 0

S1

Reset

s0

1

S2

B=0?

0

1

Shift left A,

Shift right B

Load A

Load B

b00

P<-P+A

Done

s

1

1

0

S3

Binary

1101

x 1011

--------------

1101

1101

0000

1101

---------------

10001111

Datapath circuit for the multiplier




Design

Shift- left

register

Data A

Clock

L

E

n

LA

EA

B

n

b0z

Shift-right

register

Data B

L

E

n

LB

EB

n

0

+

2nA

sum 2n 2n

0

1 0Psel

registerEEP

2n

P

2nDataP

ASM chart for the

multiplier control circuit




Design

Psel=0, EP

S1

Reset

s0

1

S2

z

0

1

Psel=1,

EA, EB

b00

EP

Done

s

1

1

0

S3

VHDL for the

multiplier circuit




Design

Part 1

VHDL for the

multiplier circuit




Design

Part 2

VHDL for the

multiplier circuit




Design

Part 3

VHDL for the

multiplier circuit




Design

Part 4

Clock Synchronization




Design

Clock

enable

circuit

clock

Dat

a D Q

Q’E

Clock Skew: If the circuit of clock enable is used,

then the flip-flops without the enable

input will observe changes in the

clock signal slightly earlier than the

flip-flops that have the enable input.

This situation , in which the clock

signal arrives at different times at

different flip-flops, is known as clock

skew.

Similar problems arise in a chip in

which the clock signal is distributed

to different flip-flops by wires whose

lengths vary appreciably.

Clock Synchronization




Design

Clock Skew: For proper operation of

synchronous sequential

circuits, it is essential to

minimize the clock skew as

much as possible.

The clock signal is

distributed to the flip-flops

such that the length of wire

between each flip-flop and

clock source is the same.

An H tree clock

distribution network

ELCT 501: Digital System Design - German …eee.guc.edu.eg/Courses/Electronics/ELCT501 Digital System...Elements used in ASM Charts Dr. Mohamed Abd el Ghany 3 Department of Electronics

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