The Allen-Bradley 1756-L55M24 is a processor module for the ControlLogix platform. ControlLogix systems provide processing, safety, motion, discrete, and drives control and enhanced I/O in a compact package. The modular architecture enables efficient design and modification. ControlLogix systems are comprised of a single chassis which houses the processor module (also called the controller) and I/O modules. A number of communications modules are available which can be installed in the system chassis to enable communication with other networks. The ControlLogix system is very flexible: multiple controllers are able to be installed in a single chassis and I/O can be installed in distributed locations and connected over I/O links.

The 1756-L55M24 can be installed in any slot in the system chassis. Furthermore, the controller can be installed or removed while the chassis power is on. However, module insertion or removal in hazardous locations is dangerous and could cause an explosion. Therefore, in hazardous locations, the system power should be removed before installing or removing the controller. The 1756-L55M24 controller has 3.5 MB of non-volatile user memory and can, therefore, be used without a battery. It has an integrated RS-232 serial port for communication. Available optional communication modules include Ethernet, DeviceNet, ControlNet, DH+, SynchLink, and Remote I/O.

The 1756-L55M24 supports the following programming languages: relay ladder, SFC, function block and structured text. Programming cables supported by the controller are the 1756-CP3 and 1747-CP3 serial cable. The backplane current draw for the 1756-L55M24 is 1.25 Amps at 5.1 Volts DC and 0.014 Amps at 24 Volts DC. The power dissipation is 5.7 W while the thermal dissipation is 19.4 BTU per hour. The controller weighs 0.36 kilograms. The 1756-L55M24 is designed for environments where the ambient temperature range is within 0 to 60 degrees Celsius and where the relative humidity is 5 to 95%.