8085 program to perform ON/OFF desired output LEDs connected at the output port B.

Here we will see how to interface PORT IC with 8085.

Problem Statement

ON/OFF desired output LEDs connected at the output port B.

Discussion

Here we will see how to On/Off LEDs at port B. We are using 8255 IC for ports. The J1 and J2 connectors to connect the 8085 and 8255. The connector pin descriptions are given below. For controlling pin, we have to set the control word, that will be used in the program.

Pin no. on J1/J2
8255 Pin
Function
1
13
PC4
2
12
PC5
3
16
PC2
4
17
PC3
5
14
PC0
6
15
PC1
7
24
PB6
8
25
PB7
9
22
PB4
10
23
PB5
11
20
PB2
12
21
PB3
13
18
PB0
14
19
PB1
15
38
PA6
16
37
PA7
17
40
PA4
18
39
PA5
19
2
PA2
20
1
PA3
21
4
PA0
22
3
PA1
23
11
PC6
24
10
PC7
25
26
+5V
26
7
GND

 

 

Group A and B will operate in mode 0.

Using port A as input port and port B as output port. The operation mode of port C is immaterial, as it will not be used here. Here the operation mode of port C is considered as input.
Thus setting the control word as (10011001)
Therefore the control word is 99 H.

Program

Address
HEX Codes
Labels
Mnemonics
Comments
8000
3E, 99
START:
MVI A, CW
Load the CW in the accumulator
8002
D3, 43
 
OUT 43 H
Output the CW to control register
8004
3E, 55
 
MVI A, 55 H
ON alternate output LEDs at port B
8006
D3, 41
 
OUT 41 H
Put the pattern byte at output port
8008
76
 
HLT
Stop

 

Updated on: 30-Jul-2019

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