6ES7321-7BH01-0AB0

Siemens 6ES7321-7BH01-0AB0 is an SM 321 digital input signal module for the SIMATIC S7-300 PLC system. It provides 16 isolated digital inputs operating at 24 V DC and uses a single 20-pole front connector. Siemens specifies the inputs according to IEC 61131 Type 2 characteristics.

The module accepts a nominal 24 V DC load voltage, with an allowable range of 20.4–28.8 V DC and reverse-polarity protection. A logical “0” is detected between -30 and +5 V, while a logical “1” corresponds to 13–30 V. Typical input current at signal “1” is approximately 7 mA.

Input delay is parameterizable at 0.1 / 0.5 / 3 / 15 / 20 ms, allowing the module to be adapted to different signal and interference conditions. The module supports diagnostic interrupts and hardware/process interrupts, with diagnostic functions configurable in the PLC hardware configuration. A red SF LED provides group fault indication.

The SM 321 also supports isochronous operation, making it suitable for applications requiring synchronized processing from the PLC application through to the input terminals. Shielded signal cables can be up to 1,000 m, while unshielded cables can be up to 600 m. Two-wire sensors are supported, with a permissible quiescent current of up to 2 mA.

Siemens currently identifies this article as a spare part. Its product phase-out began on 1 October 2023, so this lifecycle status should be considered when planning new systems or long-term spare-parts inventories.