The 1785-L40L PLC-5/40L Standard Controller with Extended I/O Link is a 48K word controller manufactured by Allen-Bradley that has extended local I/O port, which coordinates and control the operations of industrial field devices connected to it. It is installed in the leftmost slot 1771 I/O chassis, and it has a maximum I/O connection capacity of 2048 I/O. It draws 3.3A backplane current at 5V DC from the power supply of the 1771 I/O chassis, and it dissipates 17W heat when operational. The controller supports the use of the (1785-RC) Relay Cartridge, and it can be used with an Allen-Bradley compatible battery-backed memory module. The 1785-L40L supports 8 points, 16 points, 32 points, and intelligent Bulletin 1771, 1794, 1746, and 1791 I/O modules, and it will connect to external devices that are connected on the Data Highway Plus (DH+) network and on the Remote I/O network via the double DH+ or Remote I/O communication port, which is configurable for remote I/O Adapter or Scan.

The 1785-L40L has a maximum user memory of 48000 words and can assigns I/O Hardware address through the half slot addressing mode, which addresses any combination of 8, 16, and 32 I/O modules, the single slot mode, which addresses any combination of 8 and 16-point modules, with 32-point modules in I/O pairs and the double slot mode. It supports a maximum of 16 I/O racks, and it will successfully coordinate a maximum of 61 I/O chassis. The 1785-L40L can form an Extended Local I/O link when used with an extended local I/O adapter, and it will allow for a maximum of 16 extended local I/O chassis scan. The controller provides voltage isolation between the communication ports, and between the communication ports and the relay cartridge, tested at 500 Volts and 1000 Volts for 60 seconds. It has an operational temperature range between 0 and 60 degrees Celsius, and it comes in an open enclosure. The 1785-L40L weighs 1.42 kilograms, and it is UL, CE, C-TICK, and CSA-certified.