Siemens 6ES7321-1BH02-0AA0 Digital Input Module

Siemens 6ES7321-1BH02-0AA0 is a SIMATIC S7-300 digital input module (SM 321) that provides 16 isolated DC 24 V inputs for expanding a PLC’s sensing capability. It plugs into the S7-300 backplane via a single 20-pole front connector, delivering 16 channels of 24 V DC logic input signals to the CPU. Each input is designed for field signals at 24 V DC and features isolated input circuits that separate the field side from the backplane, helping protect the controller from transient spikes and noise common in industrial environments. This module is intended for use with SIMATIC S7-300 systems and integrates with Siemens’ standard software ecosystem for configuration, diagnostics, and commissioning. Typical applications include reading digital signals from pushbuttons, limit switches, proximity sensors, and other industrial sensors on automation lines, conveyors, and packaging systems. With 16 channels packed into a compact 20-pin module, the SM 321 offers a practical, space-efficient means to scale input capacity in existing S7-300 installations while maintaining compatibility with Siemens’ modular I/O approach. The exact part number 6ES7321-1BH02-0AA0 identifies this module variant, confirming its 16 DC 24 V inputs and isolated input circuits designed for DIN-rail mounted S7-300 configurations.