Allen-Bradley SLC 5/04 Processor: Hardware & Communication Guide

The Allen-Bradley SLC 5/04 processor is a modular programmable logic controller made by Rockwell Automation. It provides high-speed ladder logic execution and direct plant-floor connectivity across Data Highway Plus (DH+) networks. As a central CPU of the modular SLC 500 platform, it bridges mid-size machinery racks into supervisory networks. There, it works alongside larger PLC-5 systems.

Specifically, the SLC 5/04 stands out in the 1747 hardware ecosystem. It integrates native DH+ networking alongside an isolated RS-232 channel. As a result, it allows simultaneous supervisory communication and local programming without auxiliary communication cards.

Key Hardware Features of the SLC 5/04 Processor

Engineered for demanding discrete and process control, the hardware architecture provides critical operational capabilities:

• High-Speed Program Execution: Operates with a typical scan execution speed of 0.90 ms per 1K instructions, providing rapid response times for complex machine logic.
• Memory Configurations: Offered in three factory memory tiers: 16K words (1747-L541), 32K words (1747-L542), and 64K words (1747-L543) of battery-backed RAM with optional non-volatile EEPROM memory modules.
• Chassis & I/O Capacity: Supports up to 3 chassis (maximum 30 slots) and up to 4,096 total I/O points across digital, analog, thermocouple, and specialty modules.
• Physical Run-Mode Keyswitch: Features a three-position keyswitch (RUN, REM, PROG) allowing online ladder logic editing and program locking directly on the front bezel.
• Advanced Math & Messaging: Full support for 32-bit signed math, floating-point data types, user-defined fault routines, and peer-to-peer MSG (Message) instructions.

Communication Port Architecture: DH+ and RS-232 Channels

The primary differentiator of the SLC 5/04 is its dual independent communication channels:

• Channel 1 (Data Highway Plus – DH+): Industrial token-passing network running across Belden 9463 (Blue Hose) cable at configurable baud rates of 57.6 kbps, 115.2 kbps, and 230.4 kbps. Connects via an 8-pin mini-DIN programming socket or 3-pin Phoenix terminal for direct plant backbone routing.
• Channel 0 (RS-232 DB9 Isolated): Multi-protocol serial port supporting DF1 Full-Duplex (point-to-point SCADA/modem), DF1 Half-Duplex, DH-485 token passing, and custom ASCII communication for barcode scanners and serial printers.

Technical Hardware Specifications (1747-L541, L542, L543)

Detailed specification breakdown across the three official modular hardware models:

Modern Connectivity & Migration Options for the SLC 5/04 Processor

Rockwell Automation has discontinued the SLC 5/04 controllers: the 1747-L541 on December 31, 2021 and the 1747-L542 on March 31, 2024. Plants that still run them can keep those racks working and connect them to modern systems without rewiring:

• Plant Ethernet & SCADA Modernization: Connect Channel 1 (DH+) to the ANC-100e Gateway to bridge PLC data directly into Ignition, FactoryTalk View, AVEVA Wonderware, or modern ControlLogix Ethernet networks without an expensive 1756-DHRIO bridging chassis.
• Field Service & Laptop Programming: Instead of the 1784-U2DHP, which costs over $3,000 new, use the ANC-120e USB to DH+ Cable for instant RSLogix 500 online monitoring on 64-bit Windows 10 and 11 laptops.

For complete cable specifications, see our 1784-U2DHP Cable Guide or review the historical evolution in our SLC 500 History Article.

Setup guides: ANC-100e User’s Guide · ANC-120e User’s Guide. Application notes: Kepware KEPServerEX · Wonderware · PanelView Plus.