Siemens 6ES7 321 - 1 FH 00 - 0 AA0 CPU Module

Siemens 6ES7 321-1FH00-0AA0 is a SM321 digital input module for SIMATIC S7-300 backplane systems, delivering 16 input channels that accept AC field signals at 120/230 VAC and convert them into PLC logic states read by the CPU. Part of the SM321 family, this 16DI module expands a controller’s I/O by allowing direct wiring of 120/230 VAC sensors, pushbuttons, and switches to the S7-300 rack architecture. The exact model number identifies its function and channel count as DI16 with AC input, making it suitable for automation layouts that rely on alternating-current field devices. Common applications include machine-automation lines, packaging equipment, and process-control panels where AC-powered sensors are used for discrete signaling. In typical configurations, the SM321 plug-in module communicates over the S7-300 backplane and is paired with compatible CPUs to provide scalable digital input capacity without additional signaling hardware. This part is widely documented and traded as a replacement or repair option for SIMATIC S7-300 installations.