Clarify MCP23017 GPIO indexing in ESPHome docs

[viniciusvillas]

This update fixes the MCP23017 component documentation. Changes were made to the description of the pin mapping, clarifying that the A port is reverse-mapped. Changes were made in the example to reflect the way the component actually works (A0 is actually pin 7, because it's reverse-mapped)

Description:

Related issue (if applicable): fixes

Pull request in esphome with YAML changes (if applicable):

• esphome/esphome#<esphome PR number goes here>

Checklist:

• [ ] I am merging into next because this is new documentation that has a matching pull-request in esphome as linked above.
  or

• [ ] I am merging into current because this is a fix, change and/or adjustment in the current documentation and is not for a new component or feature.

• [ ] Link added in /components/index.rst when creating new documents for new components or cookbook.

[coderabbitai[bot]]

Walkthrough

The documentation for the MCP23017 component was updated to clarify the pin numbering scheme, specifically detailing the reverse mapping for port A and forward mapping for port B. The example configuration was also corrected to illustrate the proper pin number for A0.

Changes

File(s)	Change Summary
components/mcp230xx.rst	Clarified pin numbering scheme for MCP23017; updated example configuration for pin A0 mapping.

Sequence Diagram(s)

No sequence diagram generated as the changes are limited to documentation updates.

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[github-actions[bot]]

There hasn't been any activity on this pull request recently. This pull request has been automatically marked as stale because of that and will be closed if no further activity occurs within 7 days. Thank you for your contributions.

[clydebarrow]

Please provide some documentation to support the assertion that port A is reverse mapped.

[viniciusvillas]

Please provide some documentation to support the assertion that port A is reverse mapped.

I couldn’t find authoritative documentation for this behavior. My findings are empirical: in practice the current ESPHome documentation for the integration with the MCP23017 diverges from what the hardware actually does (the datasheet doesn’t cover ESPHome’s integration details, so this has to be inferred from real-world tests).

If there’s a canonical reference I’ve missed, I’d appreciate a pointer. If this change isn’t a fit for main, no problem—but the current documented behavior is incorrect in practice. At minimum, this PR can serve as a breadcrumb for future readers.

[clydebarrow]

I've tracked down this behavior in practice.

Well, could you detail your findings here then. The datasheet and the ESPHome implementation appear on paper to be in agreement, so if the datasheet is wrong you'll need to provide some evidence of that.

If your assertion is correct then it's certainly important for others to know that, just need something to back it up.