Product Overview
The Allen-Bradley 1785-L40C15 is a ControlNet PLC5 Programmable Logic Controller (PLC) from the classic PLC5 series. It supports up to 48K words of user memory and handles any mix of discrete I/O totaling 2048 points. With dual ControlNet ports, Data Highway Plus (DH+), Remote I/O (RIO), and serial communication, this processor is built for demanding industrial control applications.
Key Specifications
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Manufacturer: Rockwell Automation
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Processor Type: PLC-5/40C
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Max Total I/O: 2048 (any mix); 2048 Input / 2048 output (complimentary)
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Controller Memory: up to 48 Kwords
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Communication Ports: Data Highway Plus (DH+), Remote I/O (RIO), Serial, DH using 1785-KA, Two (2) ControlNet
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Battery: Allen-Bradley 1770-XYC
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Hardware Addressing: 2-slot, 1-slot, 1/2-slot
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Program Scan Time: 0.5 ms per K word (bit logic), 2 ms per K word (typical)
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Module Location: 1771-A1B, -A2B, A3B, -A3B1, -A4B chassis; left-most slot
Technical Specifications
| Attribute |
Value |
| Max User Memory Words |
48 Kilowords |
| Battery-Backed Static RAM |
Yes |
| EEPROM Program Backup Option |
Yes (using 1785-ME16, -ME32, -ME64, and -M100) |
| Protected Memory |
No |
| Max Analog I/O Forcible |
2048 |
| Max Analog I/O Nonforcible |
48000 |
| I/O Scan Time per Rack (ControlNet) |
0.5 ms (average) |
| I/O Scan Time per Rack (Universal Remote I/O) |
10 ms at 57.6 kbits/s, 7 ms at 115.2 kbits/s, 3 ms at 230.4 mbits/s |
| Max I/O Chassis Total |
125 |
| Max I/O Chassis Extended Local |
0 |
| Max I/O Chassis Universal Remote |
60 |
| RS-232-C/422-A/423-A Ports |
1 |
| Control Coprocessor Expansion Port |
Yes |
| Controller Redundancy |
Supported |
Industry Applications
The 1785-L40C15 excels in applications requiring high availability and deterministic control over ControlNet networks. Typical uses include:
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Manufacturing lines: Coordinating multiple stations with distributed I/O via Bulletin 1771, 1794, 1746, and 1791 I/O modules.
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Process control: Handling analog and discrete I/O with fast scan times for critical loops.
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Redundant systems: Using hot backup via 1785-CBHM or ControlNet Hot Backup Cartridge for high-speed processor switchover and data transfer.
Installation & Setup Guidance
Install the 1785-L40C15 in the left-most slot of a 1771-A1B, -A2B, A3B, -A3B1, or -A4B chassis. Ensure the chassis is properly grounded and power is off during installation. Connect the battery (1770-XYC) only while the processor is powered to maintain RAM contents. For redundant configurations, install the hot backup cartridge in each ControlNet processor rack and configure the network accordingly.
Maintenance & Reliability
Regularly inspect the battery and replace it every 2-3 years or as indicated by the low-battery LED. Keep the module free of dust and ensure adequate ventilation. Because the 1785-L40C15 supports battery-backed static RAM, replacing the battery with power applied prevents memory loss. Periodic checks of the ControlNet connectors and terminators help avoid communication faults.
Compatibility & Integration
This processor communicates over Data Highway Plus (DH+), Remote I/O (RIO), serial (DF1 and ASCII protocols), and ControlNet. It supports DH using 1785-KA modules and integrates with 1771, 1794, 1746, and 1791 I/O systems, including 8-, 16-, 32-point, specialty, and intelligent modules. Memory expansion is possible using 1785-ME32, 1785-ME64, or 1785-M100 modules.
Selection Guide & Purchasing Advice
Before purchasing the 1785-L40C15, verify your required I/O count, memory needs, and communication protocols. Confirm the chassis type and slot availability. If you need redundancy, ensure the hot backup cartridge is included. For a reliable supply of genuine Allen-Bradley 1785-L40C15 processors, consider PLC Source PRO as your industrial automation parts partner.