8255AC Programmable Peripheral I/O DIP-40 IC

8255AC Programmable Peripheral I/O DIP-40 IC

The 8255AC is an integrated circuit providing a programmable interface between a microprocessor and external digital devices. Encased in a 40-pin DIP package, its internal design incorporates three separate 8-bit ports: two full 8-bit data channels and one channel subdivided into two 4-bit sections. Each port can be configured under software control to act as either an input or output. A control register governs the operating mode, allowing dynamic adaptation without rewiring or hardware adjustments.

Through straightforward interfacing signals, the 8255AC communicates with the system bus, interpreting instructions from the processor to route data in or out of the selected port lines. Internally, the chip contains latches and transceivers to buffer data and synchronize signals, ensuring reliable data flow. The TTL-compatible inputs and outputs facilitate compatibility with a broad range of digital logic circuits, and its timing characteristics preserve signal integrity in typical microcomputer environments.

Despite its simplicity, the 8255AC’s architecture permits efficient multiplexing of signals, reducing the number of dedicated I/O lines required. Originating in the early microcomputer era, this device remains emblematic of modular peripheral expansion, providing a clear example of how programmable interfaces can streamline system design and support evolving configuration demands. This makes it valuable in learning environments.

Overall, The 8255A is a general-purpose programmable l/O device designed for use with Intel microprocessors. It has 24 O pins which may be individually programmed in 2 groups of 12 and used in 3 major modes of operation. In the first mode (MODE 0), each group of 12 /0 pins may be programmed in sets of 4 to be input or output. In MODE1, the second mode, each group may be programmed to have 8 lines of input or output.

Features:

• Three independent 8-bit I/O ports (Port A, Port B, and Port C), each of which can be individually programmed as input or output under software control, allowing dynamic reconfiguration without hardware changes.
• A dedicated control register that interprets control words from the CPU to select operating mode and port direction, enabling seamless switching among modes.
• Support for three distinct modes of operation:
  • Mode 0 (Basic Input/Output), where each port functions as simple, latched I/O lines.
  • Mode 1 (Strobed Input/Output), which provides handshaking signals on Port C to synchronize data transfer with external devices.
  • Mode 2 (Bi-directional Bus), available on Port A, allowing handshaked, two-way data transfer on an 8-bit bus.
• Separate read and write strobes for each port, along with individual chip‐select inputs, ensuring proper interfacing to a microprocessor bus without additional glue logic.
• Internal data latches and bus drivers that buffer I/O lines, isolating external loads from the system bus and preserving signal integrity during high-speed operations.
• TTL-compatible input and output thresholds, making the device interface-ready for a wide range of standard digital logic families.
• Separate control over the upper and lower halves of Port C (PC7–PC4 and PC3–PC0), which can be used for additional handshaking or control‐signal functions independent of Ports A and B.
• Single-chip, NMOS implementation that integrates all required logic on a 40-pin DIP, minimizing board space while providing full programmability of 24 I/O lines.

Specifications:

8255 Pin Configuration:

Dimensions:

Applications:

• Interfacing Keyboards and Displays.
• Data Acquisition Systems.
• Industrial Automation.
• Robotics.
• Communication Systems.
• Microprocessor and Microcontroller Training Kits.
• Home Automation Systems.
• Embedded Control Systems.
• Testing and Measurement Equipment.

Package Include:

• 1x 8255AC Programmable Peripheral I/O DIP-40 IC

Datasheet:

8255AC Programmable Peripheral