This document discusses programming examples for the 8255 programmable peripheral interface (PPI) chip in different modes. It provides: 1) A program to read dip switches at port B and display the reading at port A and port C using the 8255 configured in mode 0. 2) Control words to set individual bits (PC7 and PC3) on port C in bit set/reset (BSR) mode. 3) Addresses for the 3 ports (A, B, C) and control register of the 8255 when memory mapped to address 8000H.

1. MICROPROCESSOR 8085
LECTURE 28
8255 PROGRAMMING EXAMPLES FOR DIFFERENT MODES
PROF. SANDIP DAS

2. WRITE A PROGRAM FOR IC 8255 TO READ DIP SWITCHES AND
DISPLAY THE READING FROM PORT B TO PORT A AND FROM
PORT 𝐶𝐿 AT PORT 𝐶 𝑈
8255
BufferBuffer
5V
5V
CSA1
5
A1
A0
𝑀𝐸𝑀𝑅
𝑀𝐸𝑀𝑊
RESET
PA
7
PA
0
PC
7
PC
4
PC
3
PC
0
PB7
PB0

3. Port Address: Since 8255 is memory mapped I/O, suppose it is addressed at 8000H.
Then when Chip select is enabled, then port addresses of 8255 will be-
Port A- 8000H (A1=0, A0=0)
Port B- 8001H (A1=0, A2=1)
Port C- 8002H (A1=1, A2=0)
Control Register- 8003H (A1=1, A0=1)
Control Word:
D7 D6 D5 D4 D3 D2 D1 D0
1 0 0 0 0 0 1 1
Port A in
Mode 0
Port
A=
Output
Port
𝐶 𝑈 =
Output
Port B
in
Mode 0
Port
B=
Input
Port
𝐶𝐿 =
Input
I/O
mode
=83
H

4. PROGRAM:
MVI A,83H Load accumulator with the control word
STA 8003H Write word in the control register to
initialize the ports
LDA 8001H Read switches at Port B
STA 8000H Display the reading at Port A
LDA 8002H Read switches at Port C
ANI 0FH Mask the upper four bits of Port C; these bits are not input
data
RLC
RLC
RLC
RLC
STA 8002H Display data at Port 𝐶 𝑈
HLT

5. WRITE A BSR CONTROL WORD TO SET BITS PC7 AND
PC0
D7 D6 D5 D4 D3 D2 D1 D0
0 X X X Bit Select Set/Rese
t
000= Bit 0
001= Bit 1
010= Bit 2
011= Bit 3
100= Bit 4
101= Bit 5
110= Bit 6
111= Bit 7
BSR
mode Not used,
Generally set to
0
1= Set
0= Reset

6. To set PC7 control word will be
D7 D6 D5 D4 D3 D2 D1 D0
0 0 0 0 1 1 1 1 =0F
H
To set PC3 control word will be
D7 D6 D5 D4 D3 D2 D1 D0
0 0 0 0 0 1 1 1 =07
H
MVI A, 0FH Load byte in accumulator to set PC7
OUT 83H Set PC7=1
MVI A, 07H Load byte in accumulator to set PC3
OUT 83H Set PC3=1
RET