About 1785-L40B

The programmable controller 1785-L40B is a central part of every control system based on the Allen Bradley PLC-5 series. The 1785-L40B connects local, extended, and remote I/O modules on various communication interfaces into one control system. Four built-in ports are available on the 1785-L40B controller. Ports are marked as channel 1A, channel 1B, channel 2A and channel 2B. All ports can function as remote I/scanners, remote I/O adapters, and DH+ communication interfaces. DH+ communication can do remote programming and monitoring of the 1785-L40B and can create a peer-to-peer communication network between the various PLC-5, other controllers. Remote I/O connection is used for real-time data exchange between the controller and I/O, operator interface, and other devices. On the front panel of the 1785-L40B controller is a 25-pin connector marked channel 0. This is an optically isolated EIA RS232C port. Channel 0 supports ASCII and DF1 full and half-duplex master and half-duplex slave protocols. On the front panel is the green channel 0 communication indicator light. Beside channel 0, there are two 8-pin mini-DIN connectors marked as channel 1A and channel 2A, and a DH+ programming terminal connection parallel to channels 1A and 2A. There are four three-pin connectors that function as communication ports. These three-pin connectors are used for channels 1A, 1B, 2A, and 2B. All of these ports can function as remote I/O scanners, remote I/O adapters or DH+ communication ports.

All four channels that exist on the 1785-L40B can function as remote I/O scanners or remote I/O adapters. Remote I/O scanner mode is used to read and write I/O information between a controller and remote I/O device. In this mode, the 1785-L40B is a supervisory controller for other controllers that are in adapter mode and remote I/O adapter modules. When any of the four channels, 1A, 1B, 2A or 2B are in remote I/O adapter mode, the controller monitors and controls its controller-resident local I/O while communicating with the supervisory controller via a remote link. On the 1785-L40B Data Highway Plus (DH+), a link can be used on all four existing channels. DH+ communication can be used for data transfers to other PLC-5 controllers or other higher-level components of a control system. The DH+ link can program multiple PLC-5 controllers. Maximum cable length for DH+ link depends on the transmission rate. It is crucial that all devices on a DH+ link are configured to communicate at the same transmission rate. That length goes from maximal 3048m for speed 57.6 kilobits per second, to 762m for a speed of 230.4 kilobits per second. The 1785-L40B has several indicators on the front panel for easy interaction. Indicators are used for displaying various statuses of the controller. The indicator marked BATT displays the status of the battery. The indicator marked PROC indicates the controller’s current mode, it is green when the controller is in RUN mode, and red when something is wrong. The FORCE indicator is amber when I/O forces are enabled. The COMM indicator is linked with the channel 0 communication status. The indicator is green when the channel is communicating. All four communication channels, 1A, 1B, 2A, and 2B, have a dedicated status indicator.

On the front panel of the 1785-L40B is a three-position key-switch used to select the controller mode. Each position corresponds to one mode of the processor. RUN mode is used for running the controller program and enabling outputs. In RUN mode, I/O can be forced, data table values can be edited, and programs can be saved. When in RUN mode, it is impossible to create or delete a program or data file, edit online, or change modes of operation via programming software. When the 1785-L40B processor is in program mode (PROG position of key switch), outputs are disabled, and ladder files, SFC files, or data files can be created, modified, and deleted. It is possible to download and upload transfers with the memory module. Programs can be saved and restored. In program mode, the 1785-L40B processor does not scan the internal program, and the mode of operation cannot be changed with programming software. The third mode of the 1785-L40B processor work is remote mode, and it is selected by moving the key-switch to REM position. In this mode, it is possible to choose between three sub-modes: remote program, remote test, and remote run. This selection is made via programming software. When the processor is in remote run sub-mode, outputs are enabled, and programs can be saved and restored and edited while operating. Remote program sub-mode is the same as normal program mode. While in remote test sub-mode, ladder programs can be executed with disabled outputs, but ladder programs or data files cannot be created or deleted. However, programs can be saved, restored, and edited while operating. The 1785-L40B has 48000 words of memory. The controller RAM has battery backup. For program backup, an EEPROM module can be installed in the front panel slot. Various memory module capacities are available. The total number of I/O (including local I/O and universal remote I/O combined) is 2048 any mix, or 2048 inputs and 2048 complementary outputs, meaning that to use this much I/O, pairs of modules must have duplicate addresses. Maximal number of analogue I/O is 2048. 1785-L40B can utilize total of 61 I/O chassis, but the maximum is 32 per I/O link. Backplane current load of 1785-L40B is 3.3 amps at 5 Volts. The 1785-L40B cannot connect extended local I/O chassis.