Is a Legacy Processor Failure Putting Your Production Line at Risk?
When a critical ControlLogix processor goes down, every hour of downtime cuts into output and profit. The Allen-Bradley 1756-L55M23/A is a Logix5555 processor built for the Bulletin 1756 ControlLogix platform. It delivers 1.5MB of RAM plus 1.5MB of nonvolatile memory for user programs and data. This module supports large I/O counts and high-speed deterministic scan performance for demanding control applications. Rockwell Automation discontinued this model on 2011-03-31 with no planned replacement, so sourcing a tested spare quickly matters more than ever.
Technical Specifications That Matter
The 1756-L55M23/A carries 1.5MB RAM plus 1.5MB NVM, giving you room for substantial programs and data retention across power cycles. It handles up to 128,000 maximum I/O points, which suits large, distributed control architectures. Power draw is modest at 1.23A @ 5V and 14mA @ 24V, so it fits standard 1756 chassis power budgets. A battery (1756-BA1 or 1756-BATM) maintains memory backup. The processor operates from 0 to 60 C (32 to 140 F), matching the ControlLogix family range.
| 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 |
| Current @ 5V | 1.23A |
| Current @ 24V | 14mA |
| Battery | 1756-BA1 or 1756-BATM |
| Operating Temperature | 0 to 60 C (32 to 140 F) |
| Lifecycle Status | Discontinued (2011-03-31) |
Where This Processor Still Earns Its Keep
Oil and gas operations often run ControlLogix racks well beyond the original equipment lifecycle. A 1756-L55M23/A keeps those lines running when a replacement processor is the only path to restoring production. The 128,000 max I/O capacity supports large upstream and midstream control systems where many points must be scanned deterministically. Industrial automation integrators also rely on this processor for legacy skids and packaging lines that cannot justify a full platform migration. In each case, fast access to a tested spare protects throughput and avoids costly emergency retrofits.
Installation and Setup Guidance
Mount the processor in any slot of a 1756 ControlLogix chassis; the backplane provides a high-speed communication path between modules. A dedicated 1756 power supply module powers the chassis. Program and configure the unit in Studio 5000 Logix Designer (formerly RSLogix 5000). Confirm the battery is installed and healthy before commissioning, and verify that the chassis power budget covers the 1.23A @ 5V and 14mA @ 24V draw. Follow Rockwell Automation’s published installation manual for all wiring and grounding details.
Maintenance and Reliability for Legacy Racks
Because the 1756-L55M23/A is discontinued, planned maintenance is your best defense against unplanned outages. Inspect the battery periodically and replace it per the manufacturer’s schedule to protect program memory. Keep the chassis environment within the 0 to 60 C (32 to 140 F) operating range and ensure adequate ventilation. Check backplane connections during routine shutdowns. Stocking a spare processor is a practical ROI decision: one avoided downtime event typically outweighs the cost of holding a ready-to-ship unit on the shelf.
Compatibility and Integration
The 1756-L55M23/A works within the modular ControlLogix system, where any module can sit in any slot. Chassis-based communication modules support EtherNet/IP, ControlNet, DeviceNet, and DH+/Remote I/O. Integration Note: wiring into these networks may require an external gateway or connection module; confirm cables and gateways with your supplier before ordering. The processor is programmed in Studio 5000 Logix Designer, the same environment used across the ControlLogix family.
What to Verify Before You Buy
Confirm your existing base catalog is 1756-L55M23 and that your application fits within 1.5MB RAM and 128,000 max I/O. Check that your chassis power supply can deliver 1.23A @ 5V and 14mA @ 24V. Decide whether you need the 1756-BA1 or 1756-BATM battery for memory backup. Since Rockwell lists no planned replacement, verify current lifecycle status and availability with Oil AutoTech before ordering. Oil AutoTech offers hands-on technical selection help and fast-dispatch spares for oil, gas, and industrial automation applications.
Frequently Asked Questions
Is the 1756-L55M23/A still in production?
No. Rockwell Automation discontinued this model on 2011-03-31 and lists no planned replacement. Availability depends on remaining stock, so confirm with Oil AutoTech before ordering.
How much memory does this processor provide?
It offers 1.5MB of RAM plus 1.5MB of nonvolatile memory for user programs and data.
What battery does the 1756-L55M23/A use?
The processor uses a 1756-BA1 or 1756-BATM battery for memory backup.
How many I/O points can it handle?
It supports up to 128,000 maximum I/O points, suitable for large ControlLogix architectures.
Can I still program it with modern software?
Yes. Configure and program the processor in Studio 5000 Logix Designer, formerly RSLogix 5000.
Contact Oil AutoTech today for pricing and availability.
