Purchase now: Allen-Bradley 1756-L55 ControlLogix 5555 Controller
Atlantechdrives provides you the 1756-L55, a reliable and essential member of the ControlLogix 5555 family. Although considered a legacy or «end-of-life» product by the manufacturer, the 1756-L55 remains a critical component for thousands of active industrial lines worldwide. This processor is the perfect replacement for maintaining older systems without the extreme cost and risk of a full-scale controller migration.
- Memory: Expandable via 1756-M1, M2, or M3 modules
- Communication: Serial RS-232 port integrated
- I/O Capacity: Supports up to 128,000 digital / 4,000 analog points
- Tasks: 32 Tasks (multitasking operating system)
- Firmware: Compatible with various RSLogix 5000 versions
The Legacy Workhorse: Why the 1756-L55 Still Matters
The 1756-L55 was the foundation of the first wave of high-performance ControlLogix systems. Its modular memory architecture allowed plants to scale their logic by simply swapping a memory card rather than the entire CPU. Today, it is primarily used as a critical spare part. It supports the same robust backplane as the modern L7 and L8 series, meaning it can still manage modern I/O and communication modules if the firmware is updated. For facilities running on older RSLogix 5000 projects (versions 10 through 16), the 1756-L55 is often the only way to restore operations quickly after a CPU failure without rewriting significant portions of the legacy code.
Installation Advice: Memory and Battery Best Practices
When installing a replacement 1756-L55, you must ensure that your 1756-Mxx memory module is correctly seated in the side slot of the processor. Without the memory module, the CPU will not function. Additionally, because the L55 utilizes volatile SRAM for program storage, a healthy 1756-BA1 or BA2 battery is mandatory to prevent program loss during power cycles. Before inserting the module into the chassis, check the «Series» (A, B, or C) to ensure it matches your hardware requirements. We also recommend clearing the memory (cycling the battery) before downloading a new project to ensure no residual data corrupts the new program.
Maintenance and Avoiding Obsolescence Risks
Maintenance for the 1756-L55 is focused on battery management and thermal care. The «BATT» LED on the front panel should be checked daily; if it turns red, you have very little time to replace the battery before the program is erased. For long-term reliability, ensure that the industrial cabinet has clean filters and operational fans, as heat is the primary cause of ASIC failure in these older processors. By keeping a tested 1756-L55 in your spare parts inventory, you avoid the «Obsolescence Trap» where a simple CPU failure leads to weeks of downtime while waiting for a modern system migration.
FAQs
Q: Can I use the 1756-L55 with EtherNet/IP?
A: Yes, as long as you have an ENBT, EN2T, or similar communication bridge in the same chassis.
Q: What software do I need for the 1756-L55?
A: You generally need RSLogix 5000 software (version check required based on firmware).
Do you need more references from this brand? Explore our full catalog of Allen-Bradley here.
This legacy ControlLogix 5555 controller remains a robust choice for existing systems; consider expanding its I/O via a 1756-ENBT Ethernet bridge.
