Type-C Cable Orientation

The Voyager M310C was designed with optimized probe circuitry so that it can passively capture and pass through a very clean 10 Gbps signal. To achieve this goal, the system was designed with fixed pin-assignments for the primary SuperSpeed TX and RX pair. This prevents users from reversing the plug orientation on the analyzer side of the link. Some have raised concerns that there might be issues they are unable to capture in this manner. These concerns are unfounded, and it should be made clear that the plug orientation can be freely reversed on the DUT side of the link. There is no scenario that cannot be fully debugged in this manner.

Due to this design architecture, the M310C requires a bit more awareness from its users. Next to both ports is a status LED that indicates one of three states. GREEN indicates that the CC termination is detected in the proper orientation, while RED indicates that that CC termination is detected, but in the incorrect orientation. The LED will remain off if no CC connection is detected.:

Despite necessitating an extra moment’s work from the user, this implementation does not limit the test cases that they can debug. In a standard host-device environment, there are four different orientations in which one could connect a cable. This adds complexity for developers, who must multiplex the signals from these pins. It follows that they will be interested in verifying that they can correctly transmit and receive traffic in both orientations.

As seen in Figure 2-2, both ends of a cable have a CC pin (A5), from which each partner can determine the orientation. If the CC termination is detected on a receptacle’s CC1 pin (A5, in Figure 2-1), the partner knows that it will receive PD traffic over that line, and SS traffic on the TX1/RX1 pins (A2-3, B10-11). If the CC termination is instead detected on the CC2 pin (B5), the partner will receive PD traffic over that line, and SS traffic on the TX2/RX2 (A10-11, B2-3) pins.

USB traffic will always travel across a cable over a predetermined set of wires. PD traffic will traverse the CC line (A5), while SS traffic is sent across the TX1/RX1 pins (A2-3, B10-11). USB 2.0 traffic runs across the single pair of D+/D- lines (A6-7). It is the receptacle side that must determine the orientation and multiplex the signaling. Unless a user is trying test whether the analyzer does this (it doesn’t), there is no benefit to changing the orientation on the analyzer side. Remember that neither partner should be aware of an analyzer in the path, so the four cable orientations continue to be available. Users can orient the plug connecting to either partner with no consequences and, in that way, test all orientation scenarios.

Devices with captive cables are no different. As in the M310C, the lines of a captive device are hardwired internally, so the multiplexer circuitry is not necessary. Flipping the plug on the analyzer side does not change this, it simply necessitates that the analyzer be able to multiplex the signals.