The 1756-L81EXT Controller is a controller manufactured by Allen-Bradley as a member of the ControlLogix-XT controllers product series. These controllers are designed to work the same as the conventional ControlLogix controllers do. Products in the ControlLogix-XT product line comprises control components as well as communication system components which are coated conformally to add a protective layer when the controllers are exposed to corrosive and harsh environments. The Allen-Bradley 1756-L81EXT ControlLogix-XT Controller can tolerate and work in a temperature range from -20 to 70 degrees Celsius when it is used with the Flex I/O-XT series products. It can withstand a temperature range from -25 to 70 degrees Celsius when it is used on its own. The operators who have used the LXT chassis are advised to upgrade to the K version of the chassis.

Some of the main specifications and features of the 1756-L81EXT Controller include the ability to handle 32 controller tasks, 1000 programs per task, and unlimited local I/O event triggers. Like many ControlLogix controllers, the 1756-L81EXT Controller also features integral communication ports which are 1 USB port and an embedded Ethernet port. It also supports multiple communication options like the Ethernet/IP, Remote Input/Output, Data Highway Plus, DeviceNet, ControlNet, SynchLink, and the third-party process and device networks. The device also has support for multiple programming languages like the relay ladder logic, structured text, function block diagram, and sequential function chart programming languages. It operates on 3 MB of user memory and it has a thermal dissipation rating of 21.2 BTU per hour. The controller has a current draw rating of 5 milliamps at 1.2 Volts DC and 1.2 Amps at 5.1 Volts DC.