OVERVIEW

Official designation: Allen-Bradley 1775-S4A (PLC-3, I/O Scanner Programmer Interface Module)

Role/Application: This single-slot module connects the PLC-3 processor to Bulletin 1771 I/O chassis, managing data exchange across four I/O communication channels and providing an RS-232-C programming interface.

KEY SPECS SUMMARY

Power: 5 V DC from backplane

Interfaces / Ports: Four I/O channels, one RS-232-C channel

Indicators: Four status LED indicators

Operating Temp: 0 to 60 degrees C

Platform / Compatibility: PLC-3 processor systems

Limit: I/O capacity 2048 inputs/2048 outputs

Lifecycle: Discontinued/Obsolete

FREQUENTLY ASKED QUESTIONS

Technical Specifications:

Q: What are the typical I/O scan times when using a single channel on the 1775-S4A module?

A: Nominal I/O scan times for one channel range from 5.5 to 6.5 milliseconds.

Wiring & Installation:

Q: What type of cable and maximum distance are supported for I/O chassis connection from the scanner?

A: The module supports Bulletin 1771 I/O chassis up to 10,000 cable feet away via Twinaxial Cable.

Troubleshooting & Compatibility:

Q: What is the recommended direct hardware replacement module for the 1775-S4A in PLC-3 systems?

A: The 1775-S5 or 1775-SR5 scanners can replace the 1775-S4A, requiring a memory clear and auto configure via the LIST function.

Replacement & Upgrades:

Q: What is the primary modern platform recommended for full migration from the obsolete Allen-Bradley PLC-3 system?

A: The current recommended upgrade path is migration to the modern Allen-Bradley ControlLogix automation platform.