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6ES7421-1FH20-0AA0 is identified by Siemens as a Digital Input Module within the Simatic S7 family.
For replacement planning, a digital input module receives discrete on/off states from field contacts and devices, then makes those states available to the controller for monitoring, sequencing, alarms, and interlocks. The assigned system function should be preserved through installation and service.
Within an S7 installation, the exact hardware order number determines supported interfaces and configuration behavior. System and software compatibility should be checked before replacement. Application details remain governed by the exact product revision.
When this product is used for lifecycle support, technicians should confirm the installed revision, connection arrangement, and system assignment rather than assuming interchangeability with a similarly named module. This helps preserve the function assigned to the installed control node.
Active Siemens Product 11.13.2023
SIEMENS SIMATIC S7-400, digital input SM 421, isolated 16 DI; UC 120/230V inputs according to IEC1131-2 Type 2
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