1771-DCM

The Allen-Bradley 1771-DCM is a PLC 5 Direct Communication Module. It allows communication between a local processor with the remote I/O scanner port of a supervisory processor by using a remote I/O adapter port across a remote I/O link. It supports two modes of transfer i.e., discrete transfer for up to eight words or block transfer for up to 64 words with 1 status word. A supervisory processor communicates with the 1771-DCM as an adapter module and the local processor communicates over the backplane using block transfer. It has uses in various applications where the transfer of data table values is required. The 1771-DCM module has a communication rate of 57.6 Kbps and 115 Kbps. It has a backplane current load of 1.2A at 5V DC and maximum power dissipation of 6.3W. It requires a remote I/O adapter port for connection. For installation, the 1771-DCM requires one slot on the 1771 I/O chassis. Keying bands for placing it in right I/O slots are between pins 16 and 18 for the upper connector and between pins 2 and 4 for the lower connector. For wiring, the 1770-CD Belden 9463 or equivalent cable must be used. The 1771-DCM module has Power, Serial communication, Backplane communication, and Module Fault diagnostics Indicators. It supports serial communication and reads/writes data in parallel form. It has switches for options according to application requirements. It has a communication rate of 57.6K Baud up to 10,000 feet or 115.2K Baud up to 5000 feet. It has an I/O Rack Address and a Rack Size setting option for discrete data transfer. The 1771-DCM has a protected data option to prevent block transfer until the previous data transfer is completed.

The Allen-Bradley 1771-DCM is a Direct Communications module that is part of the 1771 Programmable Logic Controller (PLC) platform. This module is used to establish direct communication between supervisory and local processors via Remote I/O (RIO) communication protocol.

With this module, processors residing in the same RIO network are capable of exchanging information and process data for the purpose of monitoring and control. It supports RIO transmission speed specifically, 57.6K baud at 10,000 feet of communication cable and 115.2K baud at cable length of 5000 feet. Appropriate cable for use to establish connection between processors using the 1771-DCM is the standard RIO cable specifically, 1770-CD which is the Belden 9463 or any equivalent cable. This module can perform Discrete data transfer wherein up to 7 words + one status word can be exchanged and up to 63 words plus one status words can be transferred using the Block Transfer instruction.

The 1771-DCM may be used with PLC-2/05; PLC-2/15; PLC-2/02; PLC-2/30; PLC-3; PLC-5; PLC-5/250 processors and the 1771-ASB Remote I/O adapter. This module occupies a single-slot of the 1771 chassis. It has eight (8) DIP switches installed within this module which is used to define the operation of this module. Switch 1 is used to set Baud Rate; Switch 2 is unused; Switch 3 defines the last rack of the network; Switch 4 sets the transfer method; Switch 5 is unused; Switch 6 sets data protection while Switch 7 and Switch 8 defines the rack size such as ¼, ½. ¾ and Full rack.