SIMATIC S7-400 digital input SM 421 6ES7421-1BL01-0AA0

Overview

Signal modules are the interface of the controller to the process. 
A host of different digital and analog modules provide exactly the inputs/outputs required for each task. Digital and analog modules differ as regards the number of channels, voltage and current ranges, isolation, diagnostics and alarm functions, etc. 
However, the S7-400 signal modules are only a subset of the modules that can be connected to the S7-400 via PROFIBUS DP. 
Centrally connected signal modules can be connected and disconnected during operation. 
This makes module replacement extremely easy. 
In all the module ranges listed here, SIPLUS components are also available for corrosive atmospheres/condensation.