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3. Key Technical Specifications
| Parameter | Value |
|---|---|
| Catalog Number | 1756-L55M13 |
| Processor Type | ControlLogix 5555 (Logix5555) |
| User Memory (Data & Logic) | 1.5 MB |
| I/O Memory | 208 KB |
| Nonvolatile Memory | None (battery-backed RAM only) |
| Max Digital I/O | 128,000 points |
| Max Analog I/O | 4,000 inputs / 2,000 outputs |
| Typical Program Scan Time | 0.08 ms |
| Backplane Current @ 5.1 V DC | 1.23 A |
| Backplane Current @ 24 V DC | 0.014 A (14 mA) |
| Power Dissipation | 5.6 W |
| Thermal Dissipation | 19.1 BTU/hr |
| Battery | 1756-BA1 or 1756-BATM |
| Operating Temperature | 0…60 °C (32…140 °F) |
| Storage Temperature | –40…85 °C (–40…185 °F) |
| Relative Humidity | 5…95 % non-condensing |
| Isolation Voltage | 30 V continuous, basic insulation |
| Weight, Approx. | 0.35 kg (12.5 oz) |
| Compatible Chassis | 1756-A4, A7, A10, A13, A17 |
| Programming Software | RSLogix 5000 |
4. Product Introduction
The Allen-Bradley 1756-L55M13 is a ControlLogix 5555 processor with 1.5 MB of user memory and 208 KB of I/O memory. It executes ladder, function block, structured text, and sequential function chart logic in a standard 1756 chassis.
This controller supports up to 128,000 I/O points and a wide range of communication modules (EtherNet/IP, ControlNet, DeviceNet, DH+, etc.). It is a legacy Logix5555 platform processor that remains in service on many installed systems. New-surplus units are the practical source for replacements because the L55 series is discontinued.
1756-L55M13
1756-L55M13
5. Troubleshooting Quick Reference
| Symptom | Possible Cause | Relevance to this Part | Quick Check Method | Recommendation |
|---|---|---|---|---|
| No LEDs / dead controller | Power supply or backplane issue | ❌ Low | Measure 5.1 V and 24 V on chassis backplane | Verify chassis power supply first |
| Solid red OK LED | Major fault | ✅ High | Connect RSLogix 5000 and read fault log | Clear fault, check program and I/O configuration |
| Battery low or program lost | Weak or dead 1756-BA1 battery | ✅ High | Replace battery with power applied | Install fresh 1756-BA1; verify retention |
| Controller will not go online | Serial cable, baud, or keying mismatch | ✅ Medium | Verify 1756-CP3 cable and serial port settings | Check electronic keying and communication path |
| High memory usage faults | Project exceeds 1.5 MB user memory | ✅ High | Monitor memory usage in RSLogix 5000 | Optimize tags or upgrade to larger memory controller |
| Intermittent scan or lock-up | Marginal power or overheating | ✅ Medium | Check chassis current load and ventilation | Confirm total backplane current stays within limits |
If the controller still faults after these checks, capture the exact major/minor fault codes, series letter, and firmware revision, then contact technical support with photos of the faceplate and chassis layout.
6. Frequently Asked Questions (FAQ)
Q: Is the 1756-L55M13 still in production?
A: No. The ControlLogix L55 series was discontinued years ago. New-surplus and fully tested refurbished units are the available sources for maintaining existing systems.
Q: Does this controller have nonvolatile memory?
A: No. Program and data are retained only by the battery (1756-BA1 or 1756-BATM). Always replace the battery with power applied to avoid losing the project.
Q: What is the difference between the 1756-L55M13 and later L6x controllers?
A: The L55M13 is an older Logix5555 platform with 1.5 MB memory and no CompactFlash option. L6x controllers offer more memory, CompactFlash support, and higher performance.
Q: Can I use this controller in a redundant system?
A: Yes, provided both controllers are on the same ControlNet network and meet the redundancy requirements of the installed firmware and software version.
Q: Will my existing RSLogix 5000 project run without changes?
A: Yes, as long as the project fits in 1.5 MB and was written for a Logix5555 controller. Download the exact same .ACD file and verify the chassis configuration matches the physical hardware.
Q: What battery does it use?
A: 1756-BA1 (standard) or 1756-BATM (with battery status module). Replace every 2–5 years or when the battery LED indicates low voltage.
Q: Can I hot-swap this processor?
A: No. Always remove power from the chassis before inserting or removing the controller. Hot-swapping risks memory corruption and backplane damage.
