Product Overview
The Allen-Bradley 1785-L20C15 is a ControlNet PLC-5 processor designed for demanding industrial automation applications. As part of the PLC-5/20C series, this module integrates local, extended, and remote I/O into a unified control system, making it a versatile choice for process control challenges.
With an integrated ControlNet phase 1.5 interface, the 1785-L20C15 supports scheduled and unscheduled peer-to-peer communication with other ControlNet nodes. It also includes dedicated Data Highway Plus (DH+) ports and a configurable channel for DH+ or Remote I/O, providing flexible connectivity for programming, monitoring, and real-time data exchange.
Technical Specifications
The 1785-L20C15 offers a robust set of specifications that ensure reliable performance in control applications. Key parameters include:
| Specification |
Value |
| Manufacturer |
Rockwell Automation |
| Brand |
Allen-Bradley |
| Part Number/Catalog No. |
1785-L20C15 |
| Module Type |
ControlNet PLC-5 Processor |
| Processor |
PLC-5/20C |
| Max User Memory Words |
16 Kilowords |
| Battery-Backed Static RAM |
Yes |
| EEPROM Program Backup Option |
Yes (using 1785-ME16, -ME32, -ME64, and -M100) |
| Protected Memory |
No |
| Max Total I/O Forcible |
512 (any mix) or 384 in + 384 out (complementary), Nonforcible 3200 |
| Max Analog I/O Forcible |
512 and Nonforcible 32000 |
| I/O Scan Time Per Rack |
ControlNet I/O 0.5 ms (average); 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 |
77 |
| Max I/O Chassis Extended Local |
0 |
| Max I/O Chassis Universal Remote |
12 |
| RS-232-C/422-A/423-A Ports |
1 |
| Control Coprocessor Expansion Port |
Yes |
Applications
The 1785-L20C15 excels in real-time, high-throughput applications. Its ControlNet interface supports controller-to-controller interlocking and real-time control of I/O, drives, and valves. Common use cases include:
- Manufacturing assembly lines requiring synchronized multi-controller coordination.
- Process control systems where remote I/O scanning and data acquisition are critical.
- Material handling systems that need reliable peer-to-peer communication between PLC-5 controllers.
Installation & Setup
Mount the 1785-L20C15 in a suitable PLC-5 chassis. Ensure backplane power is adequate: the module draws 2.7 A at 5 V DC typically (3 A maximum). Connect ControlNet via the BNC coax connectors, and use the RJ-45 Network Access Port for temporary programming connections. Configure channel 1A for DH+ and channel 1B for either DH+ or Remote I/O, depending on your network architecture. Always verify that all devices on the ControlNet network use the same phase (1.5) to avoid communication issues.
Maintenance & Reliability
The 1785-L20C15 uses a lithium battery for RAM backup. Periodically check the BATT indicator; replace the battery when the red LED illuminates to prevent memory loss. Keep the module clean and ensure proper ventilation to maintain heat dissipation within the 54 BTU/hr rating. Regularly inspect cable connections and network status LEDs to ensure reliable operation.
Compatibility & Integration
This processor integrates with ControlNet phase 1.5 networks and supports DH+ communication. It is compatible with other PLC-5 controllers and can act as a scanner or adapter on Remote I/O links. The single RS-232-C/422-A/423-A port supports ASCII and DF1 protocols for serial communication. For program backup, install an EEPROM module (1785-ME16, -ME32, -ME64, or -M100) in the front-panel slot.
Buying Guide
Before purchasing, confirm your system's compatibility with ControlNet phase 1.5 and verify power requirements. For a reliable supply of genuine Allen-Bradley 1785-L20C15 modules, trust PLC Source PRO. We offer quality industrial automation parts with prompt shipping.