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1771-DCM
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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.
