The document discusses the 8155 programmable interface device. The 8155 can be used to interface I/O devices to a microprocessor like the 8085. It contains 256 bytes of RAM, three I/O ports (Ports A, B, and C), and a 14-bit timer. The 8155 is programmed by the 8085 which sends data and instruction words to configure the I/O ports and timer registers. The timer on the 8155 has two registers and can operate in four modes to generate different output waveforms.

1. TOPIC:8155
MULTIPURPOSE PROGRAMMABLE DEVICE
SUBMITTED TO:
PHILEMON DANIEL P
ASSISTANT
PROFESSOR
EC&E DEPARTMENT
NIT HAMIRPUR
SUBMITTED BY :
K SRINATH
12458
SANJAY KUMAR
12459
AZAD PATHAK
12460

2. INTRODUCTION TO 8155
• PROGRAMMABLE INTERFACE DEVICE
• USED TO INTERFACE A I/O DEVICE TO THE MICROPROCESSOR
• IT IS A MULTIFUNCTION DEVICE DESIGNED TO USE IN MINIMUM MODE SYSTEM
• IT CONTAIN RAM, I/O PORTS AND TIMER
8085
Programmable
I/O
Interface
I/O
Devices
System
Bus

3. 8155 – A MULTIPURPOSE PROGRAMMABLE
INTERFACE
• DESIGNED TO BE COMPATIBLE WITH 8085
• IT INCLUDES
• 256 BYTES OF READ/WRITE MEMORY
• THREE I/O PORTS
• PORT A
• PORT B
• PORT C
• A 14-BIT TIMER

4. BLOCK DIAGRAM - 8155
256 X 8
Static
RAM
A
B
Timer C
Port A
8
Port B
8
Port C
6
PA0-7
PB0-7
PC0-5
AD0-7 8
IO/M
RD
WR
ALE
CE
Timer CLK
TIMER OUT
Vcc (+5 V)
Vss (0 V)
RESET
I/O Devices
8085

5. APPLICATION DESIGN WITH 8155
• OBJECTIVES
• INTERFACING 8155 WITH 8085
• PROGRAMMING 8155
WHAT TYPE OF COMMANDS CAN BE GIVEN TO
8155?
• TO CONFIGURE THE I/O PORTS AS INPUT OR OUTPUT
• TO START/STOP TIMER ETC.
• TO USE HANDSHAKE MODE OR NOT

6. PROGRAMMING 8155
• 8155 IS A PROGRAMMABLE PERIPHERAL INTERFACE
• 8085 CAN SEND DATA TO 8155 USING DATA BUS
• THIS DATA CAN BE
• FOR I/O DEVICES CONNECTED TO 8155
• TIMER REGISTERS OF 8155
• INSTRUCTION/COMMAND WORD FOR 8155
• COMMANDS FOR 8155 ARE STORED IN A 8-BIT CONTROL
REGISTER INSIDE 8155

7. CONTROL WORD FOR 8155
• A COMMAND/INSTRUCTION FOR 8155 IS ALSO CALLED
CONTROL WORD
• THIS CONTROL WORD IS WRITTEN TO CONTROL REGISTER
OF 8155
• CONTROL WORD OF 8155 IS OF 8-BITS

8. THE 8155 TIMER CONSISTS OF TWO 8-BIT
REGISTERS.
1. 8-BIT LSB AND 8-BIT MSB.
2. IN THESE 16 BITS, 14 BITS ARE USED FOR COUNTER AND TWO BIT FOR MODE
SELECTION.
3. We THE can COUNTER select IS A 14 mode BIT DOWN using COUNTER. two IT CAN bits OPERATE M2 and IN 4 DIFFERENT
M1
MODES OF OPERATION.
• 00(MODE 0)- SINGLE SQUARE WAVE
• 01(MODE 1)- SQUARE WAVE
• 10(MODE 2)- SINGLE PULSE ON TC(TERMINAL COUNT)
• 11(MODE 3)- PULSE EVERY TC

9. • MODE 0: IN THIS MODE, TIMER GIVES ONLY ONE CYCLE OF SQUARE WAVE, THE
OUTPUT REMAINS HIGH FOR 1/2 COUNT AND REMAIN S LOW FOR 1/2 COUNT.
IF COUNT IS ODD IT REMAINS HIGH FOR (N+1)/2 AND LOW FOR (N-1)/2. WHERE
N IS COUNT VALUE. WAVE WIDTH DEPENDS ON TWO FACTOR: ONE IS INPUT
CLOCK PULSE FREQUENCY, AND THE OTHER IS COUNT LOADED IN COUNTER.
• MODE 1: THIS MODE IS SIMILAR TO SINGLE SQUARE WAVE IN OPERATION BUT
THE WHEN COUNTER BECOMES ZERO, THE COUNT VALUE IS AUTOMATICALLY
RELOADED. THUS IT PROVIDES CONTINUOUS SQUARE WAVE.

10. • MODE 2: THIS MODE GIVES A SINGLE CLOCK PULSE AS A OUTPUT OF THE END
OF THE COUNT THE OUTPUT IS HIGH NORMALLY, BUT IT BECOMES LOW FOR 1
CLOCK PULSE AND AGAIN IT WILL BECOME HIGH AND REMAIN HIGH.
• MODE 3: THIS MODE IS SIMILAR TO MODE 2 BUT WHEN THE COUNTER BECOMES
ZERO THE COUNT VALUE IS AUTOMATICALLY RELOADED. THUS IT PROVIDES
CONTINUOUS PULSES.

11. THANK YOU