Design Log DEC 009 legacy controller probe access pin 14 reassigned to sw led ctrl - thepinkmile/Enigma-NG GitHub Wiki

DEC-009 - Legacy Controller Probe-Access Pin 14 Reassigned to SW_LED_CTRL

  • Status: Decided
  • Date: 2025 (GND); superseded by final design (SW_LED_CTRL)
  • Category: Electrical
  • Area: Historical Controller bring-up probe-access concept

Supersession note: Historical-only. See DEC-040 for the current rule that all Diagnostics Banks are removed from the active design specs and will only be reconsidered later during the coupon implementation review.

Decision

The legacy Controller probe-access concept pin 14 was initially reassigned from 3V3_SYSTEM to GND, following the removal of the 3V3_SYSTEM rail from all BtB interconnects (see DEC-001). In the subsequent design pass that added SW_LED_CTRL (GPIO 20) to the Link-Alpha signal set, pin 14 was reallocated to SW_LED_CTRL to expose the LED-arbitration handshake at the historical bring-up probe point.

Final assignment: Legacy Controller probe-access concept pin 14 = SW_LED_CTRL (GPIO 20, CTRL → PM, HIGH = CM5 in control of SW1 RGB LED).

Rationale

  • 3V3_SYSTEM is no longer available at the Power Module side of this debug header.
  • SW_LED_CTRL is a useful bring-up observation point - it shows whether the CM5 has taken control of the RGB LED from the hardware oscillator fallback path.
  • GND is freely available on pins 19-20; a redundant GND at pin 14 added no diagnostic value.