EN
8086
MPU
DATA
RD
DEN
DT/R
ALE
BHE/S7
M/IO
AD0-AD15,
A16/S3-
A19/S6
WR
DIR
EN
G EN
ADDRESS
DECODER
8KX8
8KX8
MEMORY
CS
CS
ADDRESS
OE
WR
74LS245
74LS244
74LS373
74LS138

4
BHE*

R
1
0

8086
Minimum
Mode
A18
A0
:
D7
D6
A19
D5
D4
D3
D2
D1
D0
directly

:
mov al, 55
mov dx, 0F000h
out dx, al
:
74LS245
B0
B1
B2
B3
B4
B5
B6
B7
A0
A1
A2
A3
A4
A5
A6
A7
E DIR 5V
543210
A
1
A
1
A
1
A
1
A
1
A
1
A
9
A
8
A
7
A
6
A
5
A
4
A
3
A
2
A
1
A
0
IOW
via bidirectional
8086
Minimum
Mode
A18
A0
:
D7
D6
A19
D5
D4
D3
D2
D1
D0
What is the
problem ?

:
mov al, 55
mov dx, 0F000h
out dx, al
:
74LS373
Q0
Q1
Q2
Q3
Q4
Q5
Q6
Q7
D0
D1
D2
D3
D4
D5
D6
D7
G EN 0V
543210
A
1
A
1
A
1
A
1
A
1
A
1
A
9
A
8
A
7
A
6
A
5
A
4
A
3
A
2
A
1
A
0
IOW
8086
Minimum
Mode
A18
A0
:
D7
D6
A19
D5
D4
D3
D2
D1
D0

8086 74LS373
Data bus
74LS138
Address
bus

a
b
c
g
d
e
f
Digit -abcdefg- hex Digit -abcdefg- hex
0 -1111110- 7Eh 1 -0110000- 30h
2 -1101101- 6Dh 3 -1111001- 79h
4 -0110011- 33h 5 -1011011- 5Bh
6 -1011111- 5Fh 7 -1110000- 70h
8 -1111111- 7Fh 9 -1111011- 7Bh
A -1110111- 77h B -0011111- 1Fh
C -1001110- 4Eh D -0111101- 3Dh
E -1001111- 4Fh F -1000111- 47h

R
VCC
S1
A
R
VCC
S1
A
Toggle Switch
Push button
Switch

:
mov al, 55
mov dx, 0F000h
in al, dx
:
74LS245
B0
B1
B2
B3
B4
B5
B6
B7
A0
A1
A2
A3
A4
A5
A6
A7
E DIR 0V
543210
A
1
A
1
A
1
A
1
A
1
A
1
A
9
A
8
A
7
A
6
A
5
A
4
A
3
A
2
A
1
A
0
IOR
8086
Minimum
Mode
A18
A0
:
D7
D6
A19
D5
D4
D3
D2
D1
D0
Be careful to
the DIR
control
5V

T1 T2 T3 T4 T1 T2 T3 Tw T4
Bus Cycle Bus Cycle
One Wait State
CLK
(RD is kept high)
Mem Write I/O Output
Status Status
A(19-16)
BHE
AD(15-0) Data Out
A
A Data Out
Latch
Address
Latch
Address
ALE
Mem I/O
M / IO
Write Write
WR
Latch
Data Latch
Data
Transmit Transmit
DT/R
Disable Enable Disable Enable
DEN
Ready Ready
Wait
READY
Valid Valid
AB(19-0)
Data Out Data Out
DB(15-0)
A,BHE
A,BHE

T1 T2 T3 T4 T1 T2 T3 Tw Tw T4
Bus Cycle Bus Cycle
Two Wait States
States
CLK
Status Status
A(19-16)
BHE
A,BHE
A,BHE
(WR is kept high)
Mem Read I/O Input
A Data In A Data In
AD(15-0)
Latch
Address
Latch
Address
ALE
Mem I/O
M / IO
Read Read
RD
Receive Receive
DT/R
Disable Enable Disable Enable
DEN
Ready Ready
Wait Wait
READY
Valid Valid
AB(19-0)
Data In Data In
DB(15-0)

74LS373 Q0
Q1
Q2
Q3
Q4
Q5
Q6
Q7
G
EN
74LS373 Q0
Q1
Q2
Q3
Q4
Q5
Q6
Q7
G
EN
5
4
3
2
1
0
A 1
A 1
A 1
A 1
A 1
A 1
A9
A 8
A 7
A 6
A 5
A 4
A 3
A 2
A 1
5V
74LS245
B0
B1
B2
B3
B4
B5
B6
B7
A0
A1
A2
A3
A4
A5
A6
A7
E
DIR
5V
74LS245
B0
B1
B2
B3
B4
B5
B6
B7
A0
A1
A2
A3
A4
A5
A6
A7
E
DIR
M/ IO
WR
RD
BAD0-BAD15
SD8-SD15
DD8-DD15
DD0-DD7
SD0-SD7
8086 CPU
74LS245
SLD0
SLD1
SLS0
SLS1
IORD
IOWR
A0
BHE

M/IO RD WR BHE A0 A15 –A3 A2 A1 SLD1 SLD0 SLS1 SLS0
1 X X X X X X X 1 1 1 1
0 0 1 0 0 0 1 0 1 1 0 0
0 0 1 1 0 0 1 0 1 1 1 0
0 0 1 0 1 0 1 0 1 1 0 1
0 1 0 0 0 0 1 0 0 0 1 1
0 1 0 1 0 0 1 0 1 0 1 1
0 1 0 0 1 0 1 0 0 1 1 1
X X X X X X 0 X 1 1 1 1
TRUTH TABLE

1. Draw the complete block diagram for an 8086
Microprocessor system with 8-push button
switches and 8-LEDs in detail assigning the
switches address at (44h) and the LEDs address
at (44h) also .
3. Redraw the same block diagram if you have
32-switches and 32 –LEDs, starting with the
address (5002h) for both input and output
then write a program to read the switch
states and output them to the LEDs in
accordance.

Required Circuits in Maximum-mode
GND
AD14
AD13
AD12
AD11
AD10
AD9
AD8
AD7
AD6
AD5
AD4
AD3
AD2
AD1
AD0
NMI
INTR
CLK
GND
VCC
AD15
A16/S3
A17/S4
A18/S5
A19/S6
HOLD
HLDA
ALE
READY
RESET
BHE/S7
MN/MX
RD
WR
M/IO
DT/R
DEN
INTA
TEST
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
31
30
29
28
27
26
25
24
23
22
21
40
39
38
37
36
35
34
33
32
8086
(Vcc)
Min Mode
GND
AD14
AD13
AD12
AD11
AD10
AD9
AD8
AD7
AD6
AD5
AD4
AD3
AD2
AD1
AD0
NMI
INTR
CLK
GND
VCC
AD15
A16/S3
A17/S4
A18/S5
A19/S6
RQGT0
RQT1
QS0
READY
RESET
BHE/S7
MN/MX
RD
LOCK
S2
S1
S0
QS1
TEST
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
31
30
29
28
27
26
25
24
23
22
21
40
39
38
37
36
35
34
33
32
8086
(GND)
Max Mode

8288 BUS Controller

IO/M DT/R SSO CHARACTERISTICS
0 0 0 Code Access
0 0 1 Read Memory
0 1 0 Write Memory
0 1 1 Passive
1 0 0 Interrupt Acknowledge
1 0 1 Read I/O port
1 1 0 Write I/O port
1 1 1 Halt
Read Write Control Signals
S0
S1
S0

8086 maximum mode bus interface