Allen-Bradley 1785-L20B PLC-5/20 Processor CPU Module
Allen-Bradley 1785-L20B PLC-5/20 Processor CPU Module
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Brand:Allen Bradley PLC Item No.:Allen-Bradley 1785-L20B Product Origin:USA Product Dimensions:270 × 140 × 50 mm Product Weight:1.25 kg Payment:T/T, Western Union, Credit Card Goods_stock:15 Shipping Port:Xiamen, China Lead Time:1-3 Days Condition:Brand New And Original Warranty:1 Year Certificate:COO
The Allen-Bradley 1785-L20B is a high-performance PLC-5/20 processor CPU module engineered for mid-range and large-scale industrial automation systems. Manufactured by Rockwell Automation, this processor combines dependable PLC-5 architecture with flexible communication capability, making it a long-standing solution for manufacturing plants, material handling systems, and process control applications.
Designed for demanding industrial environments, the 1785-L20B delivers stable ladder logic execution, distributed I/O support, and reliable DH+ communication for legacy automation infrastructures that continue to operate in critical production facilities.
1 × DH+ Fixed, 1 × DH+/Remote I/O, 1 × Serial Port
Serial Standards
RS-232-C / RS-422-A / RS-423
Max Total I/O
512 (any mix)
Max Analog I/O
512
Max I/O Chassis
13 total
Remote I/O Chassis
Up to 12
Backplane Current
2.3 A @ 5V DC
Power Dissipation
12 W
Installation
1771 PLC-5 Chassis
Operating Temperature
0°C to 60°C
Physical Dimensions & Weight
Item
Value
Size (L × W × H)
270 × 140 × 50 mm
Weight
~1.0–1.25 kg
Recommended Related Models
1785-L11B – PLC-5/11 processor module
1785-L40B – higher-capacity PLC-5 controller
1785-ENET – Ethernet communication module for PLC-5 systems
1784-PCIC – PCI communication interface module
1756-L81E – modern ControlLogix replacement platform
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Applications
The 1785-L20B is widely deployed in:
Legacy factory automation systems
PLC-5 distributed control architectures
Material handling and conveyor systems
Packaging and assembly production lines
Process manufacturing control environments
Brownfield modernization and retrofit projects
Its flexible DH+ and Remote I/O capability make it especially effective in large industrial facilities operating multi-rack PLC infrastructures.
Advantages
Proven PLC-5 platform reliability for continuous industrial operation
Expanded 16K memory for more complex automation programs
Supports distributed Remote I/O architectures
Multiple embedded communication interfaces for flexible integration
Battery-backed SRAM protects application data during power loss
EEPROM backup support for enhanced program security
Rugged industrial construction for harsh environments
Ideal for maintaining and upgrading legacy automation systems
Technical FAQs
1. What is the main function of the 1785-L20B?
It serves as the primary CPU processor for PLC-5 automation systems.
2. How much user memory does it provide?
It includes 16 Kilowords of SRAM memory.
3. Does it support DH+ communication?
Yes, it includes dedicated DH+ communication capability.
4. Can it support Remote I/O systems?
Yes, it supports DH+/Remote I/O scanner and adapter functions.
5. What is the maximum I/O capacity?
Up to 512 total I/O points depending on system configuration.
6. Is the memory battery-backed?
Yes, SRAM memory is maintained using a lithium backup battery.
7. What chassis is required for installation?
It installs into a 1771 PLC-5 chassis system.
8. Is the 1785-L20B still manufactured?
It belongs to the legacy PLC-5 product family and has been discontinued in newer Rockwell strategies.
9. What software is commonly used with this processor?
RSLogix 5 and compatible PLC-5 programming software.
10. Why is this processor still used in industry?
Many factories continue relying on PLC-5 infrastructure for stable long-term production operations and phased migration projects.
