WirelessUSB™ Protocol 2.2
2.4Bind and Reconnect Timing
When the bind button on the bridge is pressed, the bridge goes into bind mode. In bind mode, the bridge uses the bind ID to communicate with any HIDs that want to bind to the system (see section Button Bind Mode on page 17 for more information on the bind ID). The bridge enables its receiver and ‘listens’ for any bind request packets from the HID, starting from channel 0. The bridge listens for approximately 320 ms on the channel, and if there is no bind request packet, it moves to the next channel in the bind channel subset (the bind channel subset consists of channels 0, 6, 12, 18, 24 … 78). It takes the bridge approximately 4.16 seconds to sequentially ‘listen’ on all 13 channels of the bind channel subset. The bridge repeats the process for up to five times before it times out and exits bind mode (time out is approximately 21 seconds). If it receives a valid bind request packet, it imme- diately responds to the request with a bind response packet and exit the bind mode.
When the bind button on the HID is pressed, the HID goes into bind mode. While in bind mode, the HID also uses the bind ID to communicate with the bridge. The HID sends a bind request packet and listens for an AutoACK packet. If the HID does not receive the AutoACK, it moves to the next chan- nel in the bind channel subset and repeats the bind request packet. It takes the HID approximately
23.4ms to sequentially hop through all 13 channels of the bind channel subset, and the HID repeats the process for up to 1000 times before it times out. Refer to Figure
Because the bridge’s and HID’s bind buttons may be pressed at different times, the HID and the bridge could be on very different channels when the two are in bind mode. However, because the HID ‘hops’ very quickly on all bind channels while the bridge stays relatively long on a channel, the bridge and HID will have multiple opportunities of being on the same channel. As a result, binding normally completes very quickly as soon as the bridge and the HID are both in bind mode (at 1.8 ms/ channel ‘hopping’ frequency of the HID and the bridge’s 320 ms/channel, the two will ‘meet’ on the same channel at least 13 times in any 320 ms period).
26 | CY4672 Reference Design Guide, Document # |
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