8085 Microprocessor
- 8085 Instruction Sets
- Addressing Modes & Interrupts
- 8085 Pin Configuration
- Microprocessor - 8085 Architecture
8086 Microprocessor
- 8086 Addressing Modes
- Microprocessor - 8086 Interrupts
- 8086 Instruction Sets
- 8086 Pin Configuration
- 8086 Functional Units
- Microprocessor - 8086 Overview
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I/O Interfacing
Microcontrollers
- Microcontrollers - 8051 Interrupts
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- 8051 Pin Description
- Microcontrollers - 8051 Architecture
- Microcontrollers - Overview
Peripheral Devices
- 8253/54 - Operational Modes
- 8253 - Programmable Interval Timer
- Intel 8255A - Pin Description
- Programmable Peripheral Interface
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8255A - Programmable Peripheral Interface
The 8255A is a general purpose programmable I/O device designed to transfer the data from I/O to interrupt I/O under certain conditions as required. It can be used with almost any microprocessor.
It consists of three 8-bit bidirectional I/O ports (24I/O pnes) which can be configured as per the requirement.
Ports of 8255A
8255A has three ports, i.e., PORT A, PORT B, and PORT C.
Port A contains one 8-bit output latch/buffer and one 8-bit input buffer.
Port B is similar to PORT A.
Port C can be sppt into two parts, i.e. PORT C lower (PC0-PC3) and PORT C upper (PC7-PC4) by the control word.
These three ports are further spanided into two groups, i.e. Group A includes PORT A and upper PORT C. Group B includes PORT B and lower PORT C. These two groups can be programmed in three different modes, i.e. the first mode is named as mode 0, the second mode is named as Mode 1 and the third mode is named as Mode 2.
Operating Modes
8255A has three different operating modes −
Mode 0 − In this mode, Port A and B is used as two 8-bit ports and Port C as two 4-bit ports. Each port can be programmed in either input mode or output mode where outputs are latched and inputs are not latched. Ports do not have interrupt capabipty.
Mode 1 − In this mode, Port A and B is used as 8-bit I/O ports. They can be configured as either input or output ports. Each port uses three pnes from port C as handshake signals. Inputs and outputs are latched.
Mode 2 − In this mode, Port A can be configured as the bidirectional port and Port B either in Mode 0 or Mode 1. Port A uses five signals from Port C as handshake signals for data transfer. The remaining three signals from Port C can be used either as simple I/O or as handshake for port B.
Features of 8255A
The prominent features of 8255A are as follows −
It consists of 3 8-bit IO ports i.e. PA, PB, and PC.
Address/data bus must be externally demux d.
It is TTL compatible.
It has improved DC driving capabipty.
8255 Architecture
The following figure shows the architecture of 8255A −
![8255A Architecture](/microprocessor/images/8255a_architecture.jpg)