Allen-Bradley 1747-L551 SLC 500 PLC Processor

Allen-Bradley 1747-L551 SLC 500 PLC Processor is a SLC 5/05 central processing unit (CPU) designed for the SLC 500 family. This Ethernet-enabled CPU provides a built-in 10BASE-T port and an on-board RS-232 serial port for DF1/DH-485 communications, enabling both local control and networked automation. It ships with 16K of user memory and is intended for use in modular SLC 500 chassis with up to 30 module slots, supporting up to 4096 digital inputs and 4096 digital outputs. Programming is done with RSLogix 500, and the unit is compatible with the standard SLC 500 I/O addressing and networking schemes. In practice, it is commonly employed for machine control, packaging lines, conveyors, and legacy system upgrades where Ethernet connectivity is advantageous while preserving compatibility with existing 1747 I/O modules. Part of the Ethernet-enabled SLC 500 processors lineup alongside 1747-L552 and 1747-L553, the L551 is documented as a Series B CPU with Processor Revision 4 on the OS501 family, offering reliable operation for industrial automation tasks, and features a program scan time around 0.9 ms and an I/O scan time around 0.225 ms, suitable for mid-range control applications.