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Allen Bradley | PLC-5 | 1771-DCM | Image

Allen Bradley | PLC-5 | 1771-DCM | Image Allen Bradley | PLC-5 | 1771-DCM | Image

Includes a PDF Electric and Supply warranty.



13 In Stock

2 Yr PDF Supply Warranty

What is Refurbished?

Repair Service


Fast Turnaround

2 Yr PDF Supply warranty


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*US continental orders placed Monday-Friday before 4:30pm EST!

Other Available Revisions for the 1771-DCM 1771-DCM/A1771-DCM/B

Common misspellings:
  • l771-DCM
  • 177l-DCM
  • 1771DCM

The Allen Bradley 1771-DCM is a Direct Communication Module for the PLC-5 system. This module occupies a single slot in the I/O chassis. The 1771-DCM moderates communication between local processors, which are mounted on the I/O chassis and the supervisory processor. Additionally, the 1771-DCM enables direct communication between a remotely configured processor and a supervisory processor. The 1771-DCM can accommodate a discrete data transfer mode with 8 words and a block data transfer mode that has 64 words, plus a single status word. The 1771-DCM uses the backplane to communicate with the processor. The processor then regards the 1771-DCM as an intelligent Input/Output module. The scanner adapter link is used by a remote processor to initiate communication to the 1771-DCM through the backplane using block transfer.


The 1771-DCM is connected to other remote I/O chassis using the trunkline or the daisy chain hook-up. When connected using the daisy chain, each I/O chassis is spliced into the serial I/O channel using a 150 Ohm resistor for termination. When the trunkline hookup is used, a dropline not exceeding 100 feet in length is used to connect the 1771-DCM to the serial Input Output channel. The 1771-XG T-connector is used to interface the dropline with the trunkline. The open ends of the trunkline are terminated using the 1770-XF terminator set. The 1771-DCM has a mechanism in place to detect invalid data, insufficient data available, excessive data available, no data available, scanner communication errors, backplane errors, backplane resets, inactive outputs, and old data. The 1771-DCM has 4 indicators (PWR, SER COM, BPLN COM and DCM FLT) that help in monitoring and troubleshooting of the module. The 1771-DCM also has communication rates of 57.6k and 115.2k for 10,000 and 5,000 feet of cable, respectively. The 1771-DCM draws a current of 1.2A from the backplane. This module has a rack size setting and an I/O rack address for discrete data transfers.


AB Direct Comm. Mod. 1771D 1771DC

PDF Electric & Supply Inc. sells new, new surplus and refurbished products which are sourced through independent channels. All warranties and support, if applicable, are with PDF Electric & Supply Inc. and not the manufacturer. PDF Electric & Supply Inc. is not an authorized distributor or representative for the listed manufacturers and makes no representations as to any quality control performed by any listed manufacturer on the products. The products listed on this website may vary as to their country of origin; the accessories, and other items included with the product; and the language used on the packaging, the parts, and any related instructions or printed material related to the products. This website is not sanctioned or approved by any manufacturer or tradename listed. Designated trademarks, brand names and brands appearing herein are the property of their respective owners.