USB4/TBT3 SB Protocol Support
Computers & ServersUSB4 / Thunderbolt 3 Sideband Channel
What is USB4/TBT3 SB?
The USB4 / Thunderbolt 3 Sideband Channel is a low-speed serial interface used by the USB4 connection manager to communicate with routers and retimers for link initialization, tunneling configuration, and power management. The sideband channel operates on dedicated sideband pins separate from the high-speed data lanes. It carries configuration space reads/writes, notification messages, and control commands that set up DisplayPort tunneling, PCIe tunneling, and USB 3.x tunneling over the USB4/Thunderbolt link. Engineers debugging USB4 docking stations, Thunderbolt peripherals, and host controllers need sideband decode to verify connection manager operations, tunnel establishment, and link negotiation.
USB4/TBT3 SB Quick Reference
| type | Serial |
| signals | Sideband pins |
| max Speed | Varies |
| features | Connection manager sideband |
Acute Instruments Supporting USB4/TBT3 SB
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See how Acute instruments capture and decode this protocol in real time. Request a demo or contact our team.
How to Analyze USB4/TBT3 SB with Acute Instruments
Connect your Acute logic analyzer to the USB4/Thunderbolt sideband pins on the connector or controller IC.
Attach a ground lead to the target board's ground reference.
In the Acute software, select the USB4/TBT3 Sideband protocol decoder and assign the sideband signals to the correct input channels.
Configure the decoder for the expected sideband protocol version.
Capture and view decoded sideband messages showing configuration space transactions, notification messages, and tunneling commands.