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Siemens SIMATIC S7-1200 SB1221 221-3BD30-0XB0 Digital Input Board

A 24 VDC, four-channel high-speed digital input signal board for a SIMATIC S7-1200 CPU.

System role

Rebuilt from individual evidence

Documented facts

Evidence limits

Siemens TIA documentation identifies this exact reference as an SB1221 input board.

The Siemens technical specification describes four 24 VDC source inputs with high-speed counting support up to 200 kHz.

This signal board receives 24 VDC digital field signals and passes them into the S7-1200 CPU.

Unknown: installation-specific compatibility, firmware, wiring and unit condition.

Exact reference
221-3BD30-0XB0
Category
PLC / CPU
Evidence checked
2026-09-11

System role

This section explains what the product does and where it acts in the surrounding system.

Function
This signal board receives 24 VDC digital field signals and passes them into the S7-1200 CPU.
System position
It sits between upstream control or power and the downstream machine or network within the S7-1200 CPU signal-board input position.
Upstream / inputs
It receives switching signals from sensors or other 24 VDC field devices.
Downstream / outputs
It sends sampled input states to the CPU process image.
Limitations
Unknown: installation-specific compatibility, firmware, wiring and unit condition.

Evidence ledger

Facts, inferences, and unknowns are kept separate.

Facts

  • Siemens TIA documentation identifies the full article 6ES7 221-3BD30-0XB0, whose exact reference suffix is 221-3BD30-0XB0, as an SB1221 input board.

    Confidence: high

  • The Siemens technical specification describes four 24 VDC source inputs with high-speed counting support up to 200 kHz.

    Confidence: high

Inferences

  • This signal board receives 24 VDC digital field signals and passes them into the S7-1200 CPU.

    Confidence: high

    Rationale: The source-backed identity and technical specification support the stated function and system position.

Unknowns

  • Unknown: installation-specific compatibility, firmware, wiring and unit condition.

    Confidence: low

    Missing evidence: A unit-specific inspection and complete installation record are not present in the captured sources.

System position diagram

Diagram showing 221-3BD30-0XB0 between upstream control or power and downstream machine or network.

Reading limit: system position only, not a wiring or safety drawing.

System path showing where 221-3BD30-0XB0 receives inputs and sends controlled outputs.

Enlarged system diagram

Diagram showing 221-3BD30-0XB0 between upstream control or power and downstream machine or network.

System path showing where 221-3BD30-0XB0 receives inputs and sends controlled outputs.

View Mermaid source
flowchart LR\n  upstream[Upstream control or power] --> product[221-3BD30-0XB0]\n  product --> downstream[Machine or network]
View diagram labels
Nodes
Upstream control or power; 221-3BD30-0XB0; Machine or network
Edges
Upstream command or power path; Controlled output or status path

Next action

The captured evidence supports this exact reference as a documented industrial component in the stated system role.

Verify host compatibility, wiring, firmware and unit condition before installation.

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