Allen-Bradley 1747-L551 SLC 500 Programmable Logic Controller

The Allen-Bradley 1747-L551 SLC 5/05 Processor delivers 16K words of user memory in a compact SLC 500 CPU with built‑in Ethernet (10Base‑T) and RS‑232 communications. It supports Channel 1 Ethernet and Channel 0 RS‑232 (DF1, ASCII, or DH‑485), enabling networked control and serial device communication in one module. Designed for use in SLC 500 racks, the 1747‑L551 accommodates up to 4,096 inputs and 4,096 outputs across a maximum of 3 chassis and 30 backplane slots, with RSLogix 500 as the programming environment. Memory is backed by options for Flash EPROM and battery‑backed RAM per the OS500‑series firmware; typical ladder logic can yield program scan times around 0.9 ms, depending on configuration. The processor operates in ambient temperatures 0°C to 60°C with 5–95% humidity (non-condensing). Power consumption varies with supply: up to 1 A at 5 V DC or up to 200 mA at 24 V DC. The 1747‑L551 is the SLC 5/05 variant of the SLC 500 family, widely used for interfacing legacy devices via RS‑232 and for basic Ethernet connectivity in mid‑tier automation tasks.