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The 6ES7421-1BL01-0AA0 is a digital input module from the SIMATIC S7-400 series by Siemens, specifically from the SM 421 module family. It is used to connect digital field signals (e.g., switches, sensors) to the automation system, enabling the programmable logic controller (PLC) to monitor and respond to external conditions. ? Functional Overview Purpose: Reads the status (ON/OFF) of external 24V DC digital signals. Integration: Plugs into an S7-400 rack, communicating with the central processing unit (CPU) via the backplane bus. Typical Use Cases: Monitoring sensors and pushbuttons Integrating with industrial devices like limit switches or proximity sensors High-channel-density input requirements in factory automation ?? Highlights High Density: 32 digital inputs on a single module, saving space and cost. Voltage Level: 24 V DC signal level for industrial compatibility. Electrical Isolation: Each input is optically isolated from the backplane, enhancing safety and reliability. Fast Input Detection: Input delay suitable for real-time control tasks. Diagnostic Capability: Built-in features for error and status monitoring.