The Allen-Bradley 1785-LT is a Programmable Logic Controller (PLC). This controller is specifically a PLC 5/15 processor that belongs to the larger family of classic PLC 5 controllers.

The 1785-LT features support for installation of up to Four (4) local racks with One (1) rack being the resident rack. For Remote I/O configuration, this processor supports up to Three (3) RIO racks wherein up to Twelve (12) physical devices are supported. It has built-in communication interfaces such as standalone Scanner port for implementing local and Remote I/O (RIO) connection. Additionally, it also has a Data Highway Plus (DH+) communication port which can be used simultaneously with the RIO port to connect to a variety of devices such as Human Machine Interface (HMI), Supervisory Control and Data Acquisition (SCADA) as well as co-processors in the network for messaging functionalities. These ports may also be used with 3rd party, non-Allen-Bradley devices.

The 1785-LT has an embedded memory amounting 6KWords which can be expanded up to 14K Words. It may also be installed with optional memory modules such as 4K RAM expansion with catalog number 1785-MR; 8 K RAM expansion with catalog number 1785-MS and 8K EEPROM with catalog number 1785-MJ.

With the equipped memory size, the 1785-LT is capable of handling up to 512 I/O of any combination or 512 inputs and 512 outputs in complimentary mode using any supported Sixteen (16) channel or Thirty-Two (32) channel I/O modules. 16-channel modules support 2-slot addressing while 1-slot addressing for 2-slot modules. IOIOIO I/O module configuration must be implemented as well to qualify the hardware configuration.

If you set the switch to the ON position, when communication errors are detected, the outputs that are connected to this chassis remain in their final state to allow the movement of the machine to continue. It is recommended that you set Switch 1 to the OFF position to remove the output energy that is connected to this chassis when any errors are detected. The maximum user memory words of this module are 6K words and this is expandable to 10K or 14K.

The operating temperature of the 1785-LT is 0-60 °C (32-140 °F). The storage temperature of this module is -40-85 °C (-40-185 °F). The relative operating and storage humidity is 5-95% without condensation. The Allen-Bradley 1785-LT has an operating shock of 30 g (3 pulses, 11 ms). The nonoperating shock is 50 g (3 pulses, 11 ms). This module has ESD immunity of 4 kV contact discharges. The Allen-Bradley 1785-LT also follows the Electromagnetic Compatibility (EMC) standards. The 1785-LT has also passed EN 50081-2 EMC - Generic Emission Standard for operation in a Part 2 - Industrial Environment.