Since USB Type-C cables have only a single CC wire for detecting orientation (Microchip USB Type-C diagram:


can an upstream (device) connect its CC1 and CC2 pins and share a single pull-down resistor?

This would prevent the device from detecting orientation (and thus using the SuperSpeed USB 3.0 lines) and so limit it to USB 2.0. But could shorting the CC pins in a receptacle actually cause damage to other devices or prevent it from operating as a 2.0 device?

  • 1
    \$\begingroup\$ Are you trying to save on 0.1c component? Connecting CC1 and CC2 together means "Audio Accessory mode". \$\endgroup\$ Jun 28 '19 at 1:07
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    \$\begingroup\$ I'm trying to save the cost of not understanding why a component appears in a schematic.The Microchip overview I linked explains in section 3.3 that active cables are signaled by resistance Ra on the CC lines, which is distinct from the resistance Rd used for orientation. \$\endgroup\$
    – lynaghk
    Jun 28 '19 at 7:44
  • \$\begingroup\$ For better understanding you better look into the original USB Type-C specifications instead of reading some limited interpretations. You will find out that there are active cables that take alternative power from the other CC pin that becomes Vconn, and multitude of "alternate modes" that also use certain combinations of both CC1 and CC2 pins. \$\endgroup\$ Jun 29 '19 at 1:27
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    \$\begingroup\$ If it's clear in the spec, can you write a full answer so I can accept it? I'm designing a receptacle, not a plug, and my reading of USB Type-C Specification Release 1.4 suggests that shorting the CC lines in my receptacle is fine. Even if a powered cable is used, table 4-42 says that electronically marked cables (of which active cables are a subset) have isolation elements to prevent Vconn from reaching the sink. \$\endgroup\$
    – lynaghk
    Jun 29 '19 at 23:51

No, the CC pins should not be tied together on Type-C receptacle. USB Type-C specifications, V1.4, has several places that deal with use of CC1 and CC2 pins.

If you are making a USb 3.x implementation, the active CC pin will tell you the right direction of Rx/Tx data MUX. Individual CC inputs on device receptacle form the entire idea of detection of plug orientation. The specs describe the process on p.165, Section as:

If the port needs to determine the orientation of the connector, it shall do so only upon entry to this state by detecting which of the CC1 or CC2 pins is connected through the cable (i.e., the CC pin that is in the SNK.Rp state).

More, on pages 162 and 163 the specs explicitly say, i.e. Section

Both CC1 and CC2 pins shall be independently terminated to ground through Rd.

Is this enough to convince you that CC pins should not be tied together?

  • \$\begingroup\$ Thanks for taking the time to explain this; I edited my question to indicate that the device only needed USB 2.0 support and thus didn't need to know orientation. Your finding in section --- "Both CC1 and CC2 pins shall be independently terminated to ground through Rd." --- makes sounds unambiguous to me. I'm curious, though, do you know what specific failure (besides disobeying the spec) would occur if the CC pins were shorted? \$\endgroup\$
    – lynaghk
    Jul 1 '19 at 5:32
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    \$\begingroup\$ The Raspberry Pi 4 shorted CC pins together, which keeps it from being charged when used with an electronically marked cable. See scorpia.co.uk/2019/06/28/… for a full explanation. \$\endgroup\$
    – lynaghk
    Jul 9 '19 at 20:40

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