Allen-Bradley 1747 Cables & Modules Guide: SLC 500 Family Reference

The Allen-Bradley 1747 series is Rockwell's catalogue prefix for SLC 500 family hardware — the chassis-based modular PLC line that dominated North-American mid-range automation through the 1990s and 2000s. Many SLC 500 panels are still in service in 2026, and inheriting one means inheriting a specific set of cables and modules that have their own quirks, obsolescence stories, and replacement strategies. This reference covers the 1747 cables and modules a maintenance engineer is most likely to encounter, RSLogix 500 connection setup, common faults, and the migration paths when an upgrade is finally forced.

The SLC 500 family in context

SLC 500 is a chassis-based modular PLC line, sized between the compact MicroLogix and the rack-based ControlLogix. A typical SLC 500 panel comprises:

• A chassis (1746-A4, 1746-A7, 1746-A10, or 1746-A13 — 4, 7, 10, or 13 slots)
• A power supply in slot 0 of the chassis (1746-P1, P2, P3, P4, P5, P7)
• A processor module (1747-L20 / L30 / L40 fixed-I/O or 1747-L511 / L514 / L524 / L532 / L541 / L542 / L543 / L551 / L552 / L553 modular)
• I/O modules in remaining slots (1746-prefixed: 1746-IB16, 1746-OB16, 1746-NI4, 1746-NO4I, etc.)

The 1747 prefix denotes processors, programming/communication accessories, and field-bus interface modules. The 1746 prefix denotes I/O modules and chassis. They share the chassis backplane.

Programming cables

1747-CP3 — DH-485 to RS-232 programming cable

The classic SLC 500 programming cable. RS-232 9-pin Sub-D on the laptop end, DH-485 on the PLC end (8-pin Mini-DIN, similar to the Mitsubishi FX programming port at first glance — but a different protocol).

In 2026, the laptop side is the problem. Most modern laptops have no RS-232 port, so the 1747-CP3 needs a USB-to-RS-232 adapter. Get one with an FTDI FT232 chip — Prolific PL2303 adapters with older HXA chips are unreliable on Windows 10 / 11 due to driver-signing changes Prolific made years ago.

Genuine 1747-CP3 vs aftermarket: the cable's electrical spec is straightforward, and aftermarket clones often work for short downloads and program reads. They sometimes fail with EEPROM transfer operations and large memory uploads. For maintenance benches, an aftermarket cable is acceptable; for production commissioning, the genuine cable is worth it.

1747-PIC — DH-485 Personal Interface Converter

The original DH-485-to-RS-232 converter, predecessor to the 1747-CP3. You'll still see it on legacy maintenance benches and in some industrial training labs. Functionally it does the same job as the 1747-CP3 — converts laptop RS-232 to DH-485 — but the PIC is a separate inline box rather than an integrated cable. Discontinued.

1747-UIC — USB-to-DH-485 converter

The modern replacement for the 1747-CP3 plus USB-to-RS-232 adapter combination. Single USB-to-DH-485 converter that talks straight to the SLC 500 from a USB-A port. The right cable to buy in 2026 if you don't already own a 1747-CP3 + serial adapter combination.

The 1747-UIC requires a Rockwell-supplied driver. The driver is signed and works on Windows 10 / 11. RSLinx Classic recognises the UIC as a DH-485 driver.

Communication and field-bus modules

1747-SDN — DeviceNet scanner

Slot-mounted DeviceNet scanner for connecting SLC 500 chassis to DeviceNet field-bus networks. Used heavily in automotive and conveyor automation. Discontinued, but still common in the field.

If a 1747-SDN fails, spares are available on the secondary market and from Rockwell parts channels, but the long-term migration story is to MicroLogix or CompactLogix with EtherNet/IP — DeviceNet is a sunsetting bus.

1747-SN — Remote I/O scanner

Slot-mounted Remote I/O scanner that talks to 1771-prefixed PLC-5-style remote I/O drops. Common in plants where SLC 500 chassis sat alongside or replaced PLC-5 systems while keeping the existing 1771 remote I/O.

1747-KE / 1747-KE2 — DH-485 to RS-232 modules

Slot-mounted DH-485 to RS-232 gateways. Used to connect modems, third-party devices, or barcode readers to the DH-485 backplane network. Discontinued; still in service.

1747-AENTR — EtherNet/IP adapter (note)

The naming here is genuinely confusing. There is a 1747-AENTR product associated with EtherNet/IP for SLC 500 environments — it provides EtherNet/IP connectivity to legacy chassis. Confirm exact compatibility with your specific chassis and processor revision before ordering, as Rockwell has shifted product lines several times. If your SLC 500 panel needs Ethernet connectivity in 2026, the more typical path is replacement with a MicroLogix 1400 or CompactLogix L18, which have built-in Ethernet — rather than retrofitting an adapter onto aging hardware.

Battery — 1747-BA / 1747-BAB

The 1747-BA (and updated 1747-BAB) battery powers the SLC 500 processor's SRAM during power-off, preserving the program and data tables. Symptoms of a flat battery:

• Battery LED on the processor front panel illuminates red or starts flashing
• Program loss after a power cycle
• Data table values reset on power-up
• "BAT LOW" alarm in RSLogix 500 status word

Procedure to replace: the SLC 500 processor must be powered up while the battery is changed, otherwise the SRAM contents wipe. Ten- to thirty-second window depending on processor model. Plan the swap when you have the program backed up to disk and an EEPROM cassette available as fallback.

Battery life is typically 5–7 years. On any SLC 500 panel you've inherited, check the battery date and replace if there's any doubt — the cost of a battery is trivial; the cost of unrecoverable program loss isn't.

RSLogix 500 connection setup

RSLogix 500 talks to SLC 500 processors via RSLinx Classic — Rockwell's communications driver layer. RSLinx must be installed and running before RSLogix 500 can browse the network.

Setting up a DF1 driver (1747-CP3)

DF1 is the protocol RSLinx uses to drive a serial cable to the SLC 500.

1. Open RSLinx Classic.
2. Communications → Configure Drivers.
3. Available Driver Types: RS-232 DF1 devices. Add New.
4. Name the driver (e.g., "AB_DF1-1").
5. Select the COM port your USB-RS232 adapter is using.
6. Auto-Configure — RSLinx queries the port and detects the SLC 500 if the cable and processor are both behaving.
7. OK; the driver shows as Running.

Setting up a DH-485 driver (1747-UIC)

1. Install the 1747-UIC driver from Rockwell's portal first.
2. RSLinx Classic → Communications → Configure Drivers.
3. Available Driver Types: 1747-PIC / AIC+ Driver or 1747-UIC USB to DH-485 cable.
4. Add New, name the driver, accept defaults.
5. The UIC enumerates and shows as Running.

Setting up an EtherNet/IP driver

For SLC 500 systems with an EtherNet/IP adapter:

1. Communications → Configure Drivers.
2. Available Driver Types: EtherNet/IP Driver.
3. Browse Local Subnet or Browse Remote Subnet, give the laptop's IP a static address on the same subnet as the panel.

Going online

In RSLogix 500: Comms → Who Active. The active driver shows the network tree; expand to find the SLC 500 processor. Right-click → Upload program (read from CPU) or Download (write to CPU). Always Upload first when you have an unknown panel — preserve the live program before doing anything.

Common faults

"No comms" after Windows 10 or 11 upgrade

Usually a driver-signing problem with the USB-to-RS-232 adapter, not a cable problem. Replace any Prolific-PL2303-based adapter with an FTDI FT232-based adapter. Reinstall the latest signed driver.

Dead battery memory loss

See the battery section above. Always extract the program before swapping a battery on an unknown panel — and confirm the battery actually needs replacing before pulling it.

Processor key-switch position issues

The SLC 500 processor has a three-position key switch: REM (Remote), RUN, and PROG. Most online operations require REM. RUN locks edits; PROG forces stop. If RSLogix 500 lets you connect but won't accept changes, check the key switch first.

EEPROM transfer pitfalls

The 1747-M11 / -M12 EEPROM modules let you transfer the program to non-volatile memory. The pitfall is forgetting to update the EEPROM after a program edit, then losing the change after a power cycle if the processor is set to load from EEPROM. After every program change, decide whether the EEPROM should be updated and act accordingly.

Sluggish or intermittent comms on long DH-485 runs

DH-485 is a multi-drop network with strict cable-length limits. Long runs (200+ metres) with poor termination cause sporadic comms errors that look like driver problems. Confirm bus termination (1747-AIC isolated link couplers handle this on segmented networks).

Migration paths

MicroLogix 1400

The natural successor for small SLC 500 panels (4-slot or 7-slot chassis with limited I/O). MicroLogix 1400 has built-in Ethernet, more memory than most SLC processors, and runs in Connected Components Workbench (free) or RSLogix 500 (the same tool you already use). For more on MicroLogix programming see the MicroLogix 1400 programming guide if you have it on the site.

CompactLogix 5370 / 5380

The right migration target for medium-to-large SLC 500 panels (10- or 13-slot chassis with extensive I/O, motion, or specialty modules). CompactLogix uses Studio 5000 (paid licence) and the IEC-style tag-based Logix architecture — a more substantial change from the SLC 500 file-and-element model.

When migration is forced

You'll be forced to migrate when:

• A specialty 1746 / 1747 module fails and is genuinely no longer available
• The processor itself fails and replacement processors are scarce
• The customer's IT department mandates Ethernet connectivity that legacy SLC can't economically deliver
• Functional safety upgrades are required and the SLC 500 doesn't carry the SIL ratings the new spec demands

Plan the migration on your timeline, not when the system fails. Document the existing program thoroughly and schedule the conversion during an extended planned outage.

Documentation sources

Rockwell's literature library still hosts SLC 500 manuals with their original publication numbers (e.g., 1747-UM011, 1747-IN013). Search by publication number directly on the Rockwell support portal. Distributor PDF caches (Allied Electronics, Newark / Farnell, Mouser) often have the same documents indexed with friendlier search.

PLCtalk forums have decades of SLC 500 troubleshooting threads — search "1747-CP3 Windows 10" and you'll find the same five issues that catch every new maintainer. The classic "PLC Programming for Industrial Automation Application" textbook still uses SLC 500 examples for ladder logic instruction; useful if you're training a junior on a panel that uses SLC 500 idioms.

Summary

The Allen-Bradley 1747 series is well past mainstream production but isn't going anywhere from working production lines until something forces its hand. Get the right cable for your laptop (1747-UIC for new tooling, 1747-CP3 plus FTDI adapter for legacy benches), keep RSLinx Classic running, watch for the battery on every panel you inherit, and plan migrations to MicroLogix 1400 or CompactLogix on a schedule rather than during an outage. For broader AB context see the Allen-Bradley PLC error codes complete reference for diagnostic codes you'll meet on the SLC 500.