Design a state machine to display a character of string HELLO using a seven segment display

1
Another Example

• Design a state machine to display a character of
  string HELLO using a seven segment display
• How many state we need?
• Five, one for each character
• In state S0 (000) we display H
• In state S1 (001) we display E
• In state S2 (010) we display L
• In state S3 (011) we display L
• In state S4 (100) we display O
• State transitions are
• S0 -gt S1
• S1 -gt S2
• S2 -gt S3
• S3 -gt S4
• S4 -gt S5

2
Example (contd.)

• Next State and Output logic tables are
• Cur Next State Output
• 0 0 0 0 0 1 0 0 0 0 1 1 0 1 1 1
• 0 0 1 0 1 0 0 0 1 1 0 0 1 1 1 1
• 0 1 0 0 1 1 0 1 0 0 0 0 1 1 1 0
• 0 1 1 1 0 0 0 1 1 0 0 0 1 1 1 0
• 1 0 0 0 0 0 1 0 0 1 1 1 1 1 1 0

3
Moore State Machine Diagram
4
Moore machine in AHDL

• SUBDESIGN moore1 (
• clk, reset, y INPUT
• z OUTPUT
• )
• VARIABLE current current
• state output
• ss MACHINE OF BITS (z)
• WITH STATES ( s0 0,
• s1 1,
• s2 1,
• s3 0)
• BEGIN
• ss.clk clk
• ss.reset reset
• TABLE
• current current next
• state input state
• ss, y gt ss

5
Mealy State Machine Diagram
0/0
6
Mealy Machine in AHDL
SUBDESIGN mealy ( clk, reset, y INPUT z
OUTPUT ) VARIABLE ss MACHINE WITH STATES (s0,
s1, s2, s3) zd NODE BEGIN ss.clk
clk ss.reset reset TABLE current current
current next state input output state
ss, y gt z, ss s0, 0 gt 0, s0 s0, 1 gt 1, s
1 s1, 0 gt 1, s1 s1, 1 gt 0, s2 s2, 0 gt
0, s2 s2, 1 gt 1, s3 s3, 0 gt 0, s3 s3, 1
gt 1, s0 END TABLE END