8155 Basic Concepts
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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.
8155 Basic Concepts
- 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.
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