PRODUCT INFORMATION
Product Overview
The Allen-Bradley 1785-L20E is a PLC-5 Controller designed for industrial automation systems. It installs into a single slot of a Bulletin 1771 I/O chassis. The processor provides 16 Kilowords of battery-backed static RAM for user logic execution. It supports up to 512 total mixed input and output points. Alternatively, it addresses 512 input and 512 output points in complementary mode. An Allen-Bradley 1770-XYC lithium battery maintains internal SRAM data retention.
Integrated communication ports include dedicated Data Highway Plus, configurable DH+ or Remote I/O, serial, and Ethernet. The controller manages up to 13 total I/O chassis across local and remote architectures. Up to 12 universal remote chassis can connect via the remote link. Optional EEPROM modules such as 1785-ME16, 1785-ME32, 1785-ME64, or 1785-M100 provide non-volatile program backup. Mechanical keying slots secure the unit in 1771 backplanes.
TECHNICAL DATA
Technical Specifications
| Parameter | Specification |
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| UPC | 612598126422 |
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| Weight | 4.38 lbs (1.98 kg) |
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| Non-Operating Temperature | IEC 60068-2-1 (Test Ab, Un-packaged Nonoperating Cold), IEC 60068-2-2 (Test Bc, Un-packaged Nonoperating Dry Heat), IEC 60068-2-14 (Test Na, Un- packaged Nonoperating Thermal Shock): –40...85 o C (– 40...185 o F) |
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| Operating Temperature | EC 60068-2-1 (Test Ad, Operating Cold), IEC 60068-2-2 (Test Bd, Operating Dry Heat), IEC 60068-2-14 (Test Nb, Operating Thermal Shock): 0...60 o C (32...140 o F) |
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| Remote I/O | 12 chassis |
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| Maximum Number of I/O Racks | 4 (0-3) |
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| Battery | 1770-XYC |
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| Memory | 16 Kwords |
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| Embedded Communication interfaces | 1 DH+ (Fixed) 1 DH+/Remote I/O (Adapter or Scanner) 1 serial port, configurable for RS-232 and 423 and RS-422A standards; Ethernet |
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| Backplane current load | 2.3 A |
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| Power Dissipation | 12 W |
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| Power Supply | 1771-P4S, -P6S, -P4S1, -P6S1 |
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| Module Type | Standard Processor |
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| Processor | PLC-5/20E |
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| Max User Memory Words | 16 Kilowords |
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| Battery-Backed Static RAM | Yes |
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| EEPROM Program Backup Option (using 1785-ME16, -ME32, -ME64, and -M100) | Yes |
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| Protected Memory | No |
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| Max Total I/O | 512 (any mix) or 512 in + 512 out (complementary) |
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| Max Analog I/O | 512 |
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| I/O Scan Time Per Rack | 10 ms at 57.6 kbits/s, 7 ms at 115.2 kbits/s, 3 ms at 230.4 mbits/s |
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| Max I/O Chassis Extended Local | 0 |
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| Max I/O Chassis Total | 13 |
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| Max I/O Chassis Universal Remote | 12 |
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| RS-232-C/422-A/423- A Ports | 1 |
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| Control Coprocessor Expansion Port | Yes |
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TECHNICAL INFORMATION
Features
- Integrated 16 Kiloword battery-backed static RAM user memory.
- Embedded Ethernet port for networked industrial communications.
- One dedicated Data Highway Plus (DH+) channel.
- One configurable DH+ or Remote I/O scanner/adapter combination channel.
- One serial port supporting RS-232, RS-422A, and RS-423 standards.
- Maximum link capacity of 512 mixed or 512 complementary I/O points.
- Control coprocessor expansion port for system enhancements.
- EEPROM backup capability via 1785-ME16, -ME32, -ME64, and -M100 modules.
TECHNICAL INFORMATION
Applications
- Industrial control installations using Allen-Bradley Bulletin 1771 I/O chassis.
- Distributed input and output processing across remote I/O networks.
- Manufacturing cell coordination requiring Ethernet and Data Highway Plus connectivity.
TECHNICAL INFORMATION
Connections / Interfaces
- One fixed Data Highway Plus (DH+) communication port.
- One selectable DH+ or Remote I/O scanner or adapter interface.
- One 25-pin D-shell serial port supporting RS-232, RS-422A, and RS-423 standards.
- One embedded Ethernet communication channel.
- One control coprocessor expansion interface.
TECHNICAL INFORMATION
Installation Guidelines
- Install the controller into the dedicated processor slot of a 1771 I/O chassis.
- Verify chassis backplane keying at pins 40-42 and 54-56 before insertion.
- Ensure compatible power supplies such as 1771-P4S, 1771-P6S, 1771-P4S1, or 1771-P6S1 are installed.
- Verify connection of the 1770-XYC lithium battery to prevent volatile memory loss.
TECHNICAL INFORMATION
Configuration Guidelines
- Set the addressing scheme to half-slot, single-slot, or double-slot mode.
- Select remote I/O transmission rates between 57.6 kbits/s, 115.2 kbits/s, and 230.4 kbits/s.
- Assign channel configurations for dedicated DH+, Remote I/O, or Ethernet operational modes.
TECHNICAL INFORMATION
Compatibility
- Installs in Bulletin 1771-A1B, 1771-A2B, 1771-A3B, 1771-A3B1, and 1771-A4B chassis.
- Supports Bulletin 1771 8-point, 16-point, and 32-point I/O modules.
- Accepts non-volatile memory backup cards 1785-ME16, 1785-ME32, 1785-ME64, and 1785-M100.
- Operates with external power supplies 1771-P4S, 1771-P6S, 1771-P4S1, and 1771-P6S1.
TECHNICAL INFORMATION
Compliance and Certifications
- CSA certified
- UL listed
- C-certified
COMPATIBILITY
Compatibility & Replacement
COMPATIBLE MODELSInstalls in Bulletin 1771-A1B, 1771-A2B, 1771-A3B, 1771-A3B1, and 1771-A4B chassis. Supports Bulletin 1771 8-point, 16-point, and 32-point I/O modules. Accepts non-volatile memory backup cards 1785-ME16, 1785-ME32, 1785-ME64, and 1785-M100. Operates with external power supplies 1771-P4S, 1771-P6S, 1771-P4S1, and 1771-P6S1.
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 chassis types are compatible with the Allen-Bradley 1785-L20E?
The module operates in 1771-A1B, 1771-A2B, 1771-A3B, 1771-A3B1, and 1771-A4B chassis assemblies.
What memory capacity does the 1785-L20E processor offer?
The controller contains 16 Kilowords of battery-backed static RAM for user program storage.
What communication interfaces are embedded on the 1785-L20E?
It provides one Ethernet channel, one fixed DH+ port, one DH+/RIO combination port, and one serial port.
Which battery module preserves the 1785-L20E controller memory?
An Allen-Bradley 1770-XYC lithium battery maintains the contents of the internal static RAM.
