What Is the 1756-L55M23/A?
The Allen-Bradley 1756-L55M23/A is a Logix5555 processor for the ControlLogix (Bulletin 1756) platform. It carries 1.5MB of RAM plus 1.5MB of nonvolatile memory, so user programs and data survive power cycles. With a maximum of 128,000 I/O, this controller suits large, demanding control applications.
Rockwell Automation discontinued this model on 2011-03-31 with no planned replacement. That makes the 1756-L55M23/A a legacy part: buyers keep existing ControlLogix lines running rather than redesigning them.
Technical Specifications
| Specification | Value |
|---|---|
| Part Number | 1756-L55M23/A |
| Manufacturer | Allen-Bradley (Rockwell Automation) |
| Series | ControlLogix / Bulletin 1756 |
| Product Type | Processor / Controller |
| RAM | 1.5MB |
| Nonvolatile Memory | 1.5MB |
| Max I/O | 128,000 |
| Backplane Current | 1.23A @ 5V, 14mA @ 24V |
| Battery | 1756-BA1 or 1756-BATM |
| Operating Temperature | 0 to 60 C (32 to 140 F) |
Why These Specs Matter
The 1.5MB RAM plus 1.5MB NVM combination gives you working memory and permanent storage in one module. Programs, recipes, and data tables stay intact through shutdowns.
The 128,000 max I/O ceiling means one processor can handle a large, distributed machine or process line. The backplane draw of 1.23A @ 5V and 14mA @ 24V tells you how to budget the 1756 power supply module. The 0 to 60 C range covers typical control-room and cabinet environments.
Where the 1756-L55M23/A Fits
This processor works in a 1756 ControlLogix chassis, where any module can sit in any slot. The ControlBus backplane moves data between modules at high speed.
- Oil and gas process skids — large I/O counts support many sensors and valves on one controller.
- Legacy line upgrades — plants with existing ControlLogix racks can swap in a matching processor instead of rebuilding the architecture.
- Water and power utilities — deterministic scan performance suits continuous process monitoring.
Compatibility and Integration
Chassis-based communication modules support EtherNet/IP, ControlNet, DeviceNet, and DH+/Remote I/O. You program and configure the processor in Studio 5000 Logix Designer (formerly RSLogix 5000).
Integration Note
Wiring into these networks may require an external gateway or connection module. Confirm cables and gateways with your supplier before ordering.
Buyer Checklist Before You Order
Because this model is discontinued, verify these points first:
- Lifecycle status — confirm current availability with Oil AutoTech before ordering.
- Memory fit — check that 1.5MB RAM and 1.5MB NVM cover your program size.
- I/O count — confirm your total point count stays under 128,000.
- Power budget — account for 1.23A @ 5V and 14mA @ 24V in the chassis.
- Battery — plan for a 1756-BA1 or 1756-BATM battery.
Please verify current lifecycle status and availability with Oil AutoTech before ordering.
Maintenance and Reliability
Inspect the processor periodically and follow the manufacturer’s safety manual. The battery is the main wear item: a depleted 1756-BA1 or 1756-BATM can put the program at risk. Keep spares on hand so a failed unit does not stop the line.
For legacy ControlLogix owners, a ready-to-ship spare protects production far better than an emergency redesign. Oil AutoTech offers fast dispatch, worldwide, with hands-on technical selection help. Contact Oil AutoTech today for pricing and availability.
