Design Log DEC 054 signal net renamed pwr but pwr but n active low suffix conformance - thepinkmile/Enigma-NG GitHub Wiki

DEC-054 - Signal Net Renamed: PWR_BUT → PWR_BUT_N (Active-Low Suffix Conformance)

  • Status: Active
  • Date: 2026-07-11
  • Category: Electrical / Net Naming
  • Area: Power Module, Controller Board, System Architecture, Software

Decision

The signal net PWR_BUT (the power key line from the Power Module to the CM5 PMIC dedicated hardware input) is renamed to PWR_BUT_N to conform with the Enigma-NG active-low suffix convention (_N) defined in design/Standards/Global_Routing_Spec.md §10.

Rationale

  • The MIC1555 U15 monostable circuit and Q5 BSS138 N-FET on the Power Module pull this signal LOW to assert a 3.01 s power key event; SW2 also pulls it LOW on manual press.
  • The CM5 PMIC receives the signal on its dedicated hardware power-key input pin, which has an internal 10 kΩ pull-up and interprets a brief LOW pulse as an orderly shutdown event.
  • FR-PM-07 (design/Electronics/Power_Module/Design_Spec.md) explicitly states "pulse CM5 PWR_BUT LOW" - active-LOW signal.
  • The _N suffix unambiguously documents the active polarity for future reviewers.

Alternatives Considered

  • Keeping PWR_BUT without a suffix - rejected; no suffix creates ambiguity and does not conform to the GRS §10 naming standard applied to all other active-low signals in this design.

Impact

  • Net rename applied in: Power_Module/Design_Spec.md, Power_Module/Board_Layout.md, Controller/Design_Spec.md, Controller/Board_Layout.md, System_Architecture.md, Software/Linux_OS/Power_Management.md, Datasheets/RPi-cm5-datasheet.md.
  • Controller/Design_Spec.md §6.1 updated to document the CM5 PMIC pin mapping and active-LOW polarity explicitly.
  • No electrical change; net renaming only.