PRODUCT INFORMATION
Product Overview
The Allen-Bradley 1771-DCM is a PLC-5 Direct Communication Module. It provides direct communication between a local processor and a supervisory processor. The module connects to the remote I/O scanner port of the supervisory controller. Local processors communicate across the 1771 chassis backplane using block transfer. The supervisory controller communicates with the module as an adapter on the remote link.
The 1771-DCM supports discrete transfer and block transfer modes. Discrete transfer supports up to seven data words plus one status word. Block transfer mode allows transmission of up to 63 words plus one status word. The unit operates at 57.6 kbaud up to 10,000 feet. It operates at 115.2 kbaud with cable lengths up to 5,000 feet. Eight internal DIP switches configure baud rate, rack size, and data protection.
TECHNICAL DATA
Technical Specifications
| Parameter | Specification |
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| Category | PLCs |
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| Product Line | PLC 5 |
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| Weight | 2.75 lbs (1.25 kg) |
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| Storage Temperature | -40 to 185oF |
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| Module Type | Direct Communication Module (DCM) |
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| Supported Protocol | Remote I/O (RIO) |
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| Transmission rate | 57.6K baud at 10,000 ft; 115.2K baud at cable length of 5000 feet |
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| Communication cable | Belden 9463 or any equivalent |
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| Transfer modes | Discrete Data Transfer; Block Transfer |
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| Discrete Data Transfer | Up to 7 Words + 1 Status Words |
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| Block Transfer data | Up to 63 Words + 1 Status Word |
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| Response Time | 15 ms |
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| Compatible Keying | Between 2 and 14; Between 16 and 18 |
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| Backplane Current | 1.2 A |
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| Operating temperature | 32 to 131oF |
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| Relative Humidity | 5-95 % |
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| Number of Bytes | 32 Kilobytes |
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| Number of Bits | 8 Kilobits |
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| Operation | BASIC Programs and C Programs |
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| Communication w/ PLC Processor | Block-Transfer w/ PLC-5 Processor |
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| Wiring Arm | 1771-WN |
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| Module Scan Time | 1.3-5 ms |
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| Coating | Conformal Coat |
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TECHNICAL INFORMATION
Features
- Transfers process data between supervisory and local processors across remote I/O links.
- Operates at selectable transmission speeds of 57.6 kbaud or 115.2 kbaud.
- Supports discrete transfer of seven data words and one status word.
- Enables block transfer of up to 63 data words and one status word.
- Includes diagnostic indicators for power, backplane communication, serial activity, and faults.
- Provides on-board DIP switches to set rack addresses, rack size, and data protection.
TECHNICAL INFORMATION
Applications
- Data exchange between local PLC-5 processors and remote supervisory scanner ports.
- Supervisory monitoring across distributed Remote I/O controller architectures.
- Processor-to-processor data table value transfer across 1771 chassis networks.
TECHNICAL INFORMATION
Connections / Interfaces
- Connects to supervisory remote I/O links using 1770-CD Belden 9463 cable.
- Interfaces with the 1771 I/O backplane for local processor communications.
- Uses the 1771-WN wiring arm for external connections.
TECHNICAL INFORMATION
Installation Guidelines
- Install the module into a single slot of any 1771 I/O chassis.
- Place upper connector keying bands between pins 16 and 18.
- Place lower connector keying bands between pins 2 and 4.
TECHNICAL INFORMATION
Configuration Guidelines
- Use Switch 1 on the eight-position DIP switch to set the baud rate.
- Configure Switch 3 to define the last rack on the network.
- Select the data transfer method using Switch 4.
- Enable or disable data protection mode with Switch 6.
- Set rack sizing to quarter, half, three-quarter, or full using Switches 7 and 8.
TECHNICAL INFORMATION
Compatibility
- Compatible with PLC-2, PLC-3, PLC-5, and PLC-5/250 processors.
- Operates alongside the 1771-ASB Remote I/O adapter module.
- Mounts in standard 1771 I/O chassis.
TECHNICAL RESOURCES
Documentation
COMPATIBILITY
Compatibility & Replacement
COMPATIBLE MODELSCompatible with PLC-2, PLC-3, PLC-5, and PLC-5/250 processors. Operates alongside the 1771-ASB Remote I/O adapter module. Mounts in standard 1771 I/O chassis.
Verify compatibility against the exact Part Number, revision and manufacturer documentation before ordering.
PART VERIFICATION
Before You Order
Industrial automation parts can share similar model names, suffixes and revisions. Confirm the complete manufacturer Part Number before purchase.
01Check Part NumberMatch the complete ordering code on the existing unit.
02Confirm RevisionCheck suffix, hardware or firmware when applicable.
03Send a Label PhotoWe can review a clear label photo when identification is uncertain.
ORDERING PROCESS
From RFQ to Dispatch
1Submit Part Number2Verify Product Identity3Confirm Stock & Condition4Issue Quotation5Dispatch & Tracking
PRODUCT FAQ
Frequently Asked Questions
What is the primary function of the Allen-Bradley 1771-DCM?
It allows direct communication between a local processor and a supervisory processor over Remote I/O.
What cable type is required for the 1771-DCM module?
The module requires 1770-CD Belden 9463 cable or an equivalent twinaxial cable.
What transmission speeds are available on the 1771-DCM?
It supports 57.6 kbaud up to 10,000 feet and 115.2 kbaud up to 5,000 feet.
What is the market reference price for the 1771-DCM?
Observed pricing is approximately $179.00 USD. This is an indicative market reference only and is not a final quotation.
