Industrial control system (ICS) operations use trusted endpoints like human machine interfaces (HMIs) and workstations to relay commands to programmable logic controllers (PLCs). Because most PLCs lack layered defenses, compromise of a trusted endpoint can drive unsafe actuator commands and risk safety-critical operation. This research presents an embedded intrusion detection system that runs inside the controller and uses header-level telemetry to detect and respond to network attacks. The system combines a semi-supervised anomaly detector and a supervised attack classifier. We evaluate the approach on a midstream oil-terminal testbed using three datasets collected during tanker-truck loading. The anomaly detector achieves zero missed attacks, corresponding to 0.998 Matthews correlation. The supervised stage attains 97.37 percent hold-out accuracy and 97.03 percent external accuracy. The embedded design adds a median of 2,031 microseconds of end-to-end latency and does not impact PLC's cycle time. The proposed architecture provides a multi-layer embedded security that meets the real-time requirements of an industrial system.

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