Description
Product Introduction
The Allen-Bradley 1785-L60B (PLC-5/60) is a high-performance, large-capacity central processing unit engineered for heavy-duty 1771 Universal I/O applications. Delivering up to 64K words of battery-backed SRAM memory and supporting up to 3,072 total I/O points across 24 remote racks, it serves as an enterprise-grade controller for complex continuous process plants, large automotive assembly lines, and refinery sub-systems.
Featuring four configurable communication channels (supporting Data Highway Plus and Universal Remote I/O scanning) alongside a dedicated RS-232/422A/423A serial port, the 1785-L60B orchestrates wide-area control networks without bottlenecking execution. It installs directly into Slot 0 of any standard 1771 chassis and accepts optional EEPROM backup modules or a 1785-ENET sidecar for TCP/IP connectivity.
Key Technical Specifications
| Parameter | Value |
| User Memory | 64K Words (SRAM, Battery-Backed) |
| Max Total I/O | 3,072 Max (Inputs or Outputs) |
| Max Remote I/O Racks | 24 Racks (Up to 23 Remote Racks via RIO Ports) |
| Backplane Current Draw | 3.3 A @ 5 VDC |
| Onboard Network Ports | Channel 1A, 1B, 2A, 2B: Configurable DH+ or Universal RIO (Scanner/Adapter) | Channel 0: Serial RS-232/422A/423A |
| Program Scan Time | 0.8 ms per 1K memory (typical) |
| EEPROM Backup Memory | Optional 1785-ME64 Non-Volatile Memory Module |
| Replacement Battery | 1770-XYC (3.0V Lithium) |
| Compatible Chassis | 1771-A1B, 1771-A2B, 1771-A3B, 1771-A4B |
Application Scenarios & The “Trench” Experience
The Trench Story
A large wastewater treatment facility running four remote 1771-ASB chassis drops experienced periodic “Rack Fault” dropouts on Channel 2B. Diagnostic LED readings on the 1785-L60B indicated communication timeout errors across distant remote racks. By accessing the CPU’s channel configuration in RSLogix 5, engineers adjusted the baud rates and channel scan list priorities across the 1785-L60B’s four channels, balancing the network load between Channel 1B and Channel 2B without having to install additional communication bridges.
Specific Applications
- Plant-Wide Process Control: Manages continuous chemical mixing, boiler systems, and multi-stage water treatment operations requiring heavy math/analog processing.
- Multi-Rack RIO Networks: Acts as the primary master scanner supervising up to 23 remote 1771-ASB or 1747-ASB chassis drops scattered across large industrial facilities.
- High-Density DH+ Backbones: Coordinates peer-to-peer inter-PLC messaging across complex multi-controller networks running on 57.6k or 230.4k DH+ trunks.
- 1785-L60B
- 1785-L60B
Transparency SOP: Quality Assurance & Testing
Every 1785- high-capacity processor undergoes rigorous testing and thermal validation prior to shipment:
- Physical & Battery Audit: We inspect card-edge backplane connectors, verify keying bracket positions, and install a brand-new 1770-XYC lithium battery.
- Memory & Boot Verification: The unit is installed into a 1771 chassis to verify cold boot routines, clear fault logs, and test the full 64K SRAM address space.
- Multi-Channel Active Network Test:
- Channels 1A/1B & 2A/2B: Each port is individually configured and tested for both DH+ communication and RIO scanning under active load.
- Channel 0 Serial: Serial communications are verified using DF1 full-duplex protocol via RSLogix 5.
- Heavy Load Rack Scanning: The processor is loaded with a complex benchmark ladder program and assigned to scan multiple remote I/O chassis simultaneously to verify backplane current stability and scan timing.
- Non-Volatile Memory Transfer Check: EEPROM read/write routines are tested using a 1785-ME64 memory module to ensure backup program retention.
The Veteran’s Tech Trap Guide
- ⚠️ Higher Backplane Current Draw (3.3 A): Unlike smaller controllers like the 1785-L20B (which draws 2.3 A), the 1785- draws 3.3 A @ 5 VDC from the chassis backplane. Ensure your chassis power supply (e.g., 1771-P7) has enough remaining power budget to support this CPU alongside high-density I/O cards.
- ❗ Channel Rotary Switch & DIP Configuration: Channels 1A–2B can be set as either DH+ or RIO Scanner/Adapter. Ensure that both the physical DIP switches on the side of the module and the software channel configurations match your exact network topology before powering up.
- ⚠️ Battery Health Monitoring: With 64K words of memory to back up, a weak battery will lead to catastrophic memory loss if power is cycled. If the front panel BATT LED illuminates red, replace the 1770-XYC lithium battery immediately while chassis power remains ON.
- ❗ EEPROM Capacity Matching: If using non-volatile backup memory, use a 1785-ME64 module to match the full 64K memory capacity of the 1785-. Smaller EEPROMs (like the 1785-ME16) cannot back up full 64K memory images.
Frequently Asked Questions
Q: What is the main difference between the 1785- and the 1785-L20B?
The features 64K Words of memory, supports up to 3,072 I/O points (24 racks), and provides 4 configurable network channels. The 1785-L20B features 16K Words of memory, supports up to 512 I/O points (4 racks), and provides 2 network channels.
Q: What is the difference between the 1785- and 1785-L60E?
The uses standard DH+/RIO coax channels and serial communication. The 1785-L60E includes an integrated 10Base-T Ethernet port built into the front panel of the controller.
Q: Which replacement battery is required for the 1785-?
It uses a standard 3.0V Lithium 1770-XYC battery assembly.
Q: How is the 1785- programmed?
Programming is performed using RSLogix 5 software connected via Channel 0 serial, a DH+ interface card (e.g., 1784-PKTX or 1784-U2DHP), or over Ethernet using an attached 1785-ENET sidecar.
Q: What warranty covers your surplus and refurbished 1785- processors?
Every 1785- controller we ship includes our full 12-month replacement warranty. If a hardware fault, backplane failure, or port defect occurs under normal operating conditions within 365 days of purchase, we replace the unit immediately from stock or issue a full refund.
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