This is an alternative approach to Josh Cook’s card and to Dustin Howett’s “EC Tool 2” expansion card. Instead of a custom PCB design, commercial off the shelf parts are used to access the embedded controller. This is not better than Cook or Howett version , but it is easier to obtain the parts. Two major parts are needed: a USB breakout board and a serial to USB interface adapter. Parts cost about $25.
I used a USB breakout card plugged into the computer USB C expansion card. No need to remove the Framework USB C expansion card, the SBU1 and SBU2 signals are passed to the external USB connector. A 1k ohm current limiting resistor was added to both the send and receive lines.
I used a DSD TECH SH-U09C3 Isolated USB to TTL Adapter to provide electrical isolation between the unit under test and the monitoring PC. This adapter electrically isolates the transmit, receive and ground signals preventing current flow between two different computer systems. Be sure to set the power jumper to 3.3V. Cover the VCC output pin with heat shrink tubing to prevent accidentally applying power to the motherboard.
A USB C breakout board with both male and female connectors was used. The male connector connects to the laptop and the female connector can be used to connect to the TTL serial adapter so a single C port can be used. A separate computer would be required for power on initialization debugging where the monitoring computer would need to be fully functioning.
5.1 k ohm pull-down resistors on CC1 and CC2 are not required because VBUS signal is not used.
