Siemens 6ES7221-1BH32-0XB0 SIMATIC S7-1200 SM 1221 Digital Input Module, 16 DI, 24 V DC, Sink/Source, Screw Terminals

For automation engineers who need a compact yet robust digital input expansion, the Siemens SM 1221 module stands out by offering 16 isolated 24 V DC inputs in a slim DIN-rail housing that integrates seamlessly with the SIMATIC S7-1200 family. Unlike basic input cards, this module supports both sinking and sourcing configurations, giving you flexibility for PNP and NPN sensors without extra wiring adapters. Its configurable input delays from 0.2 ms to 20 ms let you filter noise or capture fast pulses according to your application, while the 500 V AC isolation protects the backplane from field-side transients. The screw terminal connection ensures reliable, maintenance-friendly wiring even in high-vibration environments. With a low 2 W backplane power draw, it leaves more budget for other modules on the same CPU. The green LED status indicators provide instant diagnostics at a glance, reducing downtime during commissioning and troubleshooting. Whether you are adding inputs to a packaging machine, conveyor system, or building automation panel, this module delivers the reliability and precision expected from Siemens SIMATIC hardware. Its IP20 rating makes it suitable for control cabinets, and the wide operating temperature range of 0 to 60 °C covers most industrial settings.

Highlights

• 16 digital inputs, 24 V DC, sink/source (PNP/NPN compatible)
• 500 V AC isolation between channels and backplane bus
• Configurable input delay: 0.2 ms to 20 ms
• Screw terminals for secure, vibration-resistant connections
• Low power consumption: max 2 W from backplane
• Green LED status indicators for each input
• DIN rail mounting, IP20 protection

In daily use

Install the SM 1221 next to your S7-1200 CPU and connect up to 16 field devices such as limit switches, photoelectric sensors, or pushbuttons. The module's sink/source capability means you can wire either NPN or PNP sensors without additional interface relays. Adjust the input filter time in the TIA Portal to match your signal speed—use a short delay for high-speed counting or a longer delay to suppress contact bounce. The LEDs give you immediate confirmation of signal presence, speeding up fault-finding. Because the module draws only 2 W, you can often add multiple units to a single CPU without exceeding the power budget. The screw terminals accept wires up to 1.5 mm², and the clear labeling on the front makes wiring straightforward. For maintenance, the module can be replaced without rewiring the entire panel, as the terminal block is removable.

Full specifications

• Brand: Siemens
• Model: 6ES7221-1BH32-0XB0
• MPN: 6ES7221-1BH32-0XB0
• EAN: 6940408100404
• Product Type: Digital Input Module
• Series: SIMATIC S7-1200
• Module Designation: SM 1221
• Number of Digital Inputs: 16
• Input Voltage: 24 V DC
• Input Current (Signal '1'): Typ. 4 mA
• Input Type: Sink/Source (PNP/NPN compatible)
• Isolation: Yes, between channels and backplane bus
• Isolation Voltage: 500 V AC
• Input Delay (Configurable): 0.2 ms to 20 ms
• Permissible Cable Length (Shielded): Max. 500 m
• Permissible Cable Length (Unshielded): Max. 150 m
• Power Consumption (from backplane): Max. 2 W
• Mounting Type: DIN Rail
• Operating Temperature: 0 to 60 °C
• Storage Temperature: -40 to 70 °C
• Connection Type: Screw terminals
• Status Indicators: Green LED for input status
• Degree of Protection: IP20
• Firmware Update Capability: Yes, via CPU

Final note

Engineered for seamless integration with SIMATIC S7-1200, the SM 1221 digital input module delivers dependable signal acquisition in a compact, industrial-grade package.