he PLC 1747-DCM is a direct communication module. The module interfaces the SLC 500 controller with the PLC in a distributed processing setup by connecting I/O adapters and controllers. In an application where distributed controllers are used, the 1747-DCM provides each Input/Output with an interface with the remote Input/Output supervisory controller for communication. The Direct Communication Module is used in a remote I/O network and it uses the Belden 9463 cable for wiring purposes. The 1747-DCM draws a current of 360 mA at 5 Volts and 0 mA at 24 Volts from the backplane, has a minimum and maximum thermal dissipation of 1.80 Watts.
The 1747-DCM module has two LED indicators, FAULT and COMM. When the FAULT indicator is on (red) it symbolizes an internal fault. This is corrected by replacing the module (when it stays on for longer after you have powered up the module). It can also be used to cycle power to the DCM’s Input Output chassis. A blinking FAULT indicator shows a configuration error. A normal state of the 1747-DCM direct communication module is indicated when the FAULT indicator is OFF. The COMM indicator is ON (green) when the module is in normal working state. It blinks if the processor (RIO scanner) is in test fault/program mode. The indicator is OFF when either the RIO scanner’s processor is; rack inhibited, not connected to the scanner or has lost communication with the DCM. To initiate communication between the supervisory and distributed processors, the 1747-DCM has two addresses; for the SLC (specified by DCM’s physical installation slot) and another one for the supervisory scanner (DCM’s logical rack address determined by DCM switches 1-6).
