1747-L543 — SLC 5/04 Modular Processor, 64K Memory, DH+ and RS-232

The 1747-L543 is the top-memory SLC 5/04 processor for the 1746-series modular chassis, offering 64K words of battery-backed user memory alongside a built-in Data Highway Plus (DH+) port and an RS-232 port. It runs the full SLC 5/04 instruction set across up to three chassis and 30 I/O module slots, supporting up to 4096 discrete inputs and 4096 discrete outputs in the largest configurations.

Specifications

Parameter	Value
Part Number	1747-L543
Processor	SLC 5/04
User Memory	64K words (60K program/data, 4K data only)
Port 0	DH+ (3-wire terminal)
Port 1	RS-232 (DF1, ASCII)
Max I/O Points	4096 discrete inputs / 4096 discrete outputs
Max Chassis / Slots	3 chassis / 30 slots
Programming Instructions	107
Scan Time	~0.9 ms/K (typical)
Memory Backup	Battery-backed RAM; optional Flash EPROM module
Programming Software	RSLogix 500

DH+ in the SLC 5/04 — Why It Still Matters

Where the 5/03 series relies on DH-485 as its native multi-drop network, the 5/04's built-in DH+ port connects it directly to legacy PLC-5 processors, programming terminals, and other DH+ devices on facility networks that predate Ethernet-based architectures. For plants with an existing DH+ backbone tying together PLC-5 and SLC 500 systems across multiple areas, the 1747-L543 slots into that network without needing a separate bridge module — a meaningful advantage when standardizing a maintenance spares strategy for an installed base that's still running mixed PLC-5/SLC hardware.

The RS-232 port runs independently for DF1 point-to-point connections to HMIs or SCADA hosts, or ASCII mode for serial peripherals. Running DH+ on one port and DF1 on the other simultaneously is a standard, fully supported configuration — the processor doesn't require choosing one network type over the other.

FAQ

Q: Can the 1747-L543 communicate over EtherNet/IP without additional hardware?

No. The 5/04 has no native Ethernet port. An external 1761-NET-ENI or similar Ethernet interface converter is required for Ethernet connectivity, bridged through the RS-232 port.

Q: Does the 64K memory program need to fit a specific chassis configuration?

No. Program size is limited by the 64K memory itself, not by the specific I/O configuration of the chassis it's developed on — programs can be transferred between compatible processors regardless of exact I/O layout, provided the target processor's memory and I/O capacity accommodate the program.

Q: Is the DH+ port compatible with the same cabling used for DH-485?

No. DH+ uses its own 3-wire cable specification distinct from DH-485 wiring — the two networks are not interchangeable at the cable or connector level.

Q: Can a smaller-memory SLC 5/04 program be loaded onto this 64K processor?

Yes. A program written for a smaller-memory 5/04 (16K or 32K) loads and runs on the 64K unit without modification, since the instruction set is identical across the 5/04 memory variants.

1747-L543 New Original 1747L543 Ser C SLC 500 CPU Processor Unit Module