The Texas Instruments LM3S6918-IBZ50-A2 is a 32-bit ARM Cortex-M3 microcontroller from the Stellaris® 6000 series, clocked at 50 MHz.
50 MHz core — enough for control-plus-connectivity
The 50 MHz Cortex-M3 core delivers enough throughput to run a lightweight TCP/IP stack (like lwIP) while handling local sensor polling and PWM outputs. It is not a high-end application processor — you are not running Linux on it — but for a dedicated control node that reports over Ethernet, the speed is well matched to the peripheral set.
Obsolete — sourcing reality and replacement path
Texas Instruments has marked the LM3S6918-IBZ50-A2 as Obsolete. That means no further factory orders are accepted; the only channel for this exact order code is the surplus and independent-distribution market.
Package and layout note
The 38 general-purpose I/O are mapped to the outer balls — check the pinout diagram for Ethernet-specific ball assignments before laying out the magnetics.