Module Overview
The Siemens 6ES7421-1BL00-0AA0 is a digital input module for the SIMATIC S7-400 programmable logic controller family. It accepts 24 VDC field signals from sensors, pushbuttons, and limit switches and presents them to the CPU backplane.
Where It Fits in the System
The module mounts in a standard S7-400 rack (UR1/UR2) and connects to the backplane via the P-bus. It is a 32-channel input module, so it occupies one slot and draws its power from the rack backplane — no separate loop supply needed beyond the 24 VDC field power.