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We have a host CCG3PA PD controller (DFP) connected to a second (UFP) PD controller via a USB-C cable with an embedded EMCA chip (CMG1). Normally, when the CCG3PA is plugged into the UFP PD controller with this cable, CCG3PA can read the data from the EMCA (CMG1) chip, as well as communicate with the UFP PD controller over CC wire.
However, if CCG3PA is plugged into the CMG1 EMCA cable only (so no UFP device connected on the other side), is it possible that CCG3PA can read the data from the CMG1 EMCA chip without an UFP present? I tried this setup with the Cypress PD Analyzer, but I didn’t see any CC packet exchanged.
No, the DFP (Downward facing port) controller cannot read the data in the EMCA chip when no UFP (Upward facing port) is connected.
The series of events in Power delivery contract goes as follows,
" The Rpand Rd termination resistors (Rp resistor in DFP and Rd resistor in UFP) on the Type-C receptacle CC pins make it possible to detect the connection event and identify the orientation of the Type-C plugs in the receptacles. The DFP and UFP monitor both CC pins on the Type-C receptacle for a voltage change from their unterminated voltages to detect the connection event. The UFP also monitors for VBUS as a second indicator of a DFP connection. Both DFP’s and UFP’s can determine the Type-C cable plug orientation on their respective ends of the connection. This is possible because only one of the CC pins is connected through the cable. After the connection and orientation is detected, the other CC pin is repurposed by the DFP as VCONN for powering the electronics in the USB Type-C EMCA plug if an Ra termination resistor is detected."
Since the EMCA chip is powered up only after there is a contract between DFP and UFP controllers, the cable capabilities cannot be determined when no UFP is connected.
An example scenario between DFP and UFP is shown below,