MC68B50CP Asynchronous Communications Interface Adapter

Updated: 2026-09-16

Overview

The MC68B50CP is a legacy asynchronous communications interface adapter (ACIA) developed by Motorola for serial data transmission in microprocessor-based systems. It serves as a bridge between parallel bus architectures and serial communication protocols like RS-232. Designed for the 6800 processor family, this IC became widely adopted in 1980s industrial controls and computer peripherals due to its flexible baud rate selection (up to 1 Mbps) and interrupt capabilities. While newer solutions have largely replaced it, the MC68B50CP remains relevant for maintaining legacy equipment.

Structure and Working Principle

The device integrates transmitter/receiver buffers, control registers, and status monitoring circuits on a single CMOS chip. It converts parallel data from the host CPU into serial output (and vice versa) using internal shift registers. Clock generation is handled either by an external crystal oscillator or an external baud rate input. The control register allows configuration of data format (5-8 bits), parity, and stop bits. Interrupt signals alert the processor to transmission completion or received data availability.

Key Features

Full-duplex operation enables simultaneous transmission and reception, while double-buffered design prevents data overrun. The programmable baud rate divider supports common rates from 110 to 1,000,000 bps without external components. Error detection includes parity, framing, and overrun checks. The 3-state outputs facilitate bus sharing, and the +5V single-supply operation simplifies system integration. Industrial-grade versions (MC68B50CP) operate across -40°C to +85°C.

Application Areas

Primary historical applications included industrial process controls, point-of-sale terminals, and early computer modems. Today, it's mainly used for: 1. Legacy system maintenance in manufacturing plants 2. Retro computing hardware projects 3. Educational demonstrations of serial communication principles 4. Niche embedded systems requiring Motorola 6800 compatibility

Maintenance and Precautions

When working with the MC68B50CP, observe ESD precautions during handling. Ensure power supply voltages remain within ±5% of 5V to prevent latch-up. For noisy environments, implement proper signal filtering on communication lines. Periodically check for oxide buildup on legacy system contacts. In replacement scenarios, verify the suffix (CP denotes commercial/industrial temperature range) matches the original specification. Thermal management is rarely needed due to low power dissipation.

B2B Procurement Guide

When sourcing MC68B50CP chips, specify whether you require new old stock (NOS), refurbished, or aftermarket units. Authentic Motorola-branded devices command premium pricing but offer guaranteed specifications. Key verification steps include testing baud rate accuracy and interrupt functionality. For batch purchases exceeding 100 units, expect 10-30% cost reduction. Lead times vary significantly; authorized distributors may require 4-8 weeks for special orders. Consider alternative ACIA chips like the 6551 for non-legacy applications.