I’m working on a carrier card for the AGX Orin where we have 4 USB ports but also need a Key E M.2 (which has a USB D pair). I am looking to use a basic two port USB 2 hub controller to share one of the diff pairs between 2 of these 5 options but there are some considerations that affect this decision. Can I share a D pair between a port that is host mode and one that is device mode (these are constant based on port)? Can I share only the D pairs between two USB3.x connections, while the Tx and Rx pairs remain directly connected to the module (except the Tx caps)? Can I share the D pair between a USB 2 connector and the USB 2 pins on the M.2 Key E expansion slot? Do any of these options require specialized controllers to achieve? (except USB3, because that would just be a USB3 hub)
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I’ll provide a comprehensive answer to your questions.
Sharing a D pair between a host-mode port and a device-mode port
In general, it’s not recommended to share a D pair between a host-mode port and a device-mode port. The reason is that the host-mode port is expected to provide power and control the data transfer, while the device-mode port is expected to receive power and respond to the host’s requests. Sharing a D pair between these two modes could lead to conflicts and instability.
However, if you’re using a USB 2 hub controller, it might be possible to share the D pair between a host-mode port and a device-mode port, but you’ll need to ensure that the hub controller can handle the different modes correctly. You may need to consult the datasheet of your specific hub controller to see if it supports this configuration.
Sharing only the D pairs between two USB3x connections
Yes, it’s possible to share only the D pairs between two USB3x connections while keeping the Tx and Rx pairs directly connected to the module. This is because the D pairs are used for USB 2.0 data transfer, while the Tx and Rx pairs are used for USB 3.x data transfer. By sharing only the D pairs, you can allow two USB3x connections to share the same USB 2.0 data path.
However, you’ll need to ensure that the hub controller can handle the USB 3.x data transfer correctly, and that the Tx and Rx pairs are properly connected to the module. You may also need to consider the impact of sharing the D pairs on the overall system performance.
Sharing the D pair between a USB 2 connector and the USB 2 pins on the M2 Key E expansion slot
Yes, it’s possible to share the D pair between a USB 2 connector and the USB 2 pins on the M2 Key E expansion slot. This is because both the USB 2 connector and the M2 Key E expansion slot use the same USB 2.0 data transfer protocol.
In this case, you can use a basic two-port USB 2 hub controller to share the D pair between the two ports. The hub controller will handle the USB 2.0 data transfer between the two ports, and you can connect the Tx and Rx pairs directly to the module.
Specialized controllers
Except for USB 3.x, which requires a USB 3.x hub controller, the other options do not require specialized controllers. A basic two-port USB 2 hub controller should be sufficient for sharing the D pair between two USB 2 connectors or between a USB 2 connector and the USB 2 pins on the M2 Key E expansion slot.
However, if you’re planning to use USB 3.x, you’ll need a USB 3.x hub controller that can handle the higher speeds and data transfer protocols of USB 3.x.
In summary:
- Sharing a D pair between a host-mode port and a device-mode port is not recommended, but might be possible with a specific hub controller.
- Sharing only the D pairs between two USB3x connections is possible, but requires careful consideration of the system performance and hub controller capabilities.
- Sharing the D pair between a USB 2 connector and the USB 2 pins on the M2 Key E expansion slot is possible using a basic two-port USB 2 hub controller.
- Except for USB 3.x, specialized controllers are not required for these configurations.
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Sorry, this is not possible.
Can I share only the D pairs between two USB3.x connections, while the Tx and Rx pairs remain directly connected to the module (except the Tx caps)?
This is not supported either.
Can I share the D pair between a USB 2 connector and the USB 2 pins on the M.2 Key E expansion slot?
You could connect one pair to a Hub and then connect the signal out from this hub.
However, the signal from this hub could not form another port with other USB3 signal.
You could connect one pair to a Hub and then connect the signal out from this hub.
However, the signal from this hub could not form another port with other USB3 signal.
It sounds like so long as the USB 2 hub has it’s two output signals to a USB 2 connector (it doesn’t have the pins for USB 3) and the M.2 Key E pins, it would work, it that correct?
Yes, correct.
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