5
4
3
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EGR 270
Fundamentals of Computer Engineering
File: Modseq.opj
Modified Sequence Counter
D
Purpose: A counter has been designed to count in the sequence 0, 2, 1, 3, 7, 5, 6, and repeat using
JK flip-flops and the excitation table method. See the attached sheet for the details of the design.
D
A Digital Clock was used to generate a 1kHz input to clock the counter. Additionally, PSPICE requires that synchronous
devices be initialized, so another Digital Clock is used to briefly provide a LOW pulse to initialize the counter to 3 (use
ClearA, Preset B, and PresetC to preset to 011). The unused Preset and Clear lines must be tied HIGH.
Analysis: A TRANSIENT analysis with a final time of 10ms is used to show ten output counts since the period of the clock is 1ms (1/1kHz).
Note: The HI input is available by
pressing the GND icon on the toolbar
and then selecting $D_HI/SOURCE
1
3
U1A
C
4
J
1
7476
CLK
2
7408
PRE
2
HI
U4A
K
Q
Q
A
15
(MSB)
14
U7A
B
J
1
7476
CLK
1
3
U2A
4
16
2
K
CLR
HI
PRE
2
3
16
CLR
C
Note: The results of the design by
the excitation table method are as
follows:
JA = BC
KA = C'
KB = A + C'
JB = 1
JC = A' + B
KC = A + B'
Q
Q
B
15
B
14
3
7432
HI
2
U6A
3
7408
U5A
CLOCK
1
1
7476
CLK
16
3
2
7408
OFFTIME = 50ms DSTM2
ONTIME = 25ns
CLK
DELAY = 10ns
STARTVAL = 1
OPPVAL = 0
J
K
3
A
OFFTIME = .5ms DSTM1
ONTIME = .5ms
CLK
DELAY = 0
STARTVAL = 0
OPPVAL = 1
HI
U3A
4
CLR
2
PRE
1
Q
Q
C
15
14
A
Title
<Title>
INIT
Size
A
Date:
5
4
3
Document Number
<Doc>
Monday, April 03
2
Rev
<RevCode>
Sheet
of
1
1
1
** circuit file for profile: Transient
Date/Time run: 04/03 22:32:27
Temperature: 27.0
(A) Modified Sequence Counter with the counting sequence 0,2,1,3,7,5,6 and repeat
CLOCK
A
B
C
COUNT
3
0s
7
2ms
5
6
0
4ms
2
6ms
1
3
8ms
7
5
10ms
Time
Date: April 03
Page 1
Time: 22:34:45
** circuit file for profile: Transient
Date/Time run: 04/03 22:32:27
Temperature: 27.0
(A) Zooming in on the initialization pulse shows the counter being initialized to count 3
INIT
CLOCK
A
B
C
COUNT
X
0s
Date: April 03
3
100ns
200ns
300ns
Time
Page 1
400ns
500ns
600ns
Time: 22:38:41
Example: Design a modified sequence counter using the excitation table method that will count in the
sequence 0,2,1,3,7,5,6, and repeat. Treat unused count 4 as a "don't care". Use JK flip-flops.
Circuit Excitation Table
A
0
0
0
0
1
1
1
1
Present State
B
0
0
1
1
0
0
1
1
C
0
1
0
1
0
1
0
1
A
0
0
0
1
X
1
0
1
Next State
B
C
1
0
1
1
0
1
1
1
X
X
1
0
0
0
0
1
JA
0
0
0
1
X
X
X
X
KA
X
X
X
X
X
0
1
0
Flip-flop Inputs
JB
KB
1
X
1
X
X
1
X
0
X
X
1
X
X
1
X
1
JC
0
X
1
X
X
X
0
X
KC
X
0
X
0
X
1
X
0
JK Flip-flop Excitation Table
Q(t)
0
0
1
1
Q(t+1)
0
1
0
1
J
0
1
X
X
K
X
X
1
0
Flip-flop Input Functions and Circuit Output Functions
BC
A 00 01 11 10
0 0 0 1 0
X
1
X
X
X
BC
A 00 01 11 10
0 1 1 X X
1
JA = BC
BC
A 00 01 11 10
0 X X X X
1
X
0
0
1
KA = C'
X
1
X
X
BC
A 00 01 11 10
0 0 X X 1
1
JB = 1
X
X
X
X
0
JC = A'B
BC
A 00 01 11 10
0 X X 0 1
1
X
1
1
KB = A + C'
BC
A 00 01 11 10
0 X 0 0 X
1
X
1
0
KC = AB'
X