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.
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.