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3. Key Technical Specifications
| Parameter | Value |
|---|---|
| Processor Type | SLC 5/04 |
| User Memory | 16K words total |
| Max Discrete I/O | 4096 inputs + 4096 outputs |
| Max Local Analog I/O | 480 |
| Max Local Chassis / Slots | 3 chassis / 30 slots |
| Program Scan Time | 0.9 ms/K typical |
| I/O Scan Time | 0.225 ms typical |
| Communication Ports | Channel 1: DH+; Channel 0: RS-232 (DF1 / DH-485 / ASCII / Modbus) |
| Memory Backup | Battery-backed RAM (1747-BA); optional flash modules |
| Backplane Current @ 5 V DC | 1.0 A |
| Backplane Current @ 24 V DC | 200 mA |
| Installation Slot | Slot 0 only |
| Operating Temperature | 0 °C to +60 °C |
| Storage Temperature | –40 °C to +85 °C |
4. Product Introduction
The Allen-Bradley 1747-L541 is the 16K-memory version of the SLC 5/04 processor. It installs in Slot 0 of any 1746 modular chassis and supports up to three local chassis with a total of 30 I/O modules.
It provides DH+ networking on Channel 1 for multi-processor systems and an RS-232 port on Channel 0 that can be configured for DF1, DH-485, ASCII, or Modbus. Typical program scan time is 0.9 ms per K of logic with an I/O scan of 0.225 ms. The processor supports remote I/O when paired with a scanner module and includes battery-backed RAM for program retention.
1747-L541
1747-L541
5. Troubleshooting Quick Reference
| Symptom | Possible Cause | Relevance to this Part | Quick Check Method | Recommendation |
|---|---|---|---|---|
| No RUN LED, chassis powered | Processor not seated or insufficient backplane power | ✅ High | Reseat in Slot 0; measure 5 V and 24 V rails | Confirm power supply capacity ≥ 1 A @ 5 V |
| CPU FAULT LED on | Memory corruption, hardware fault, or battery failure | ✅ High | Clear faults in RSLogix 500; check BATTERY LOW LED | Replace battery or reload program; replace if persistent |
| DH+ network offline | Incorrect node address, baud rate, or cable fault | ✅ High | Verify node address and baud (57.6 / 115.2 / 230.4 K); check blue-hose cable | Match network settings; inspect terminators |
| Cannot establish RS-232 comms | Wrong channel configuration or cable | ✅ High | Confirm Channel 0 protocol and baud in software; use 1747-CP3 cable | Match software settings to port configuration |
| Program lost after power cycle | Dead battery | ✅ High | Check BATTERY LOW LED; measure battery voltage | Replace 1747-BA battery |
| Remote I/O faults | Scanner module or configuration error | ❌ Low | Verify scanner configuration and RIO cable | Check scanner and adapter settings |
If the fault remains unresolved, capture LED status, fault codes, and communication parameters before contacting support.
6. Frequently Asked Questions (FAQ)
Q: Is the 1747-L541 still available new from Rockwell? No. The SLC 500 platform is discontinued. Units available today are New Surplus or refurbished. Confirm current stock and condition before ordering.
Q: What is the difference between the 1747-L541, L542, and L543? Memory size only: L541 = 16K words, L542 = 32K words, L543 = 64K words. Communication ports, I/O capacity, and scan performance are identical.
Q: Does the 1747-L541 support remote I/O? Yes. It supports remote I/O when used with a compatible scanner module (such as 1747-SN or 1747-BSN) in the local chassis.
Q: What battery does the 1747-L541 use? The standard lithium battery is the 1747-BA. It provides multi-year program retention. Replace it when the BATTERY LOW LED illuminates.
Q: Can Channel 0 be used for DH-485? Yes. The RS-232 port (Channel 0) can be configured for DH-485, DF1 Full-Duplex, ASCII, or Modbus RTU. An interface converter (such as 1761-NET-AIC) is typically required for DH-485 networking.
Q: Where must the 1747- be installed? It must be installed in Slot 0 of the primary 1746 chassis. It will not operate in any other slot.
Q: Why is New Surplus priced lower than original list? These are genuine Allen-Bradley processors from excess inventory or cancelled projects. They are unused and typically supplied with anti-static protection. They are not refurbished unless specifically stated.
