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20 CY4672 Reference Design Guide, Document # 001-16968 Revision **
WirelessUSB™ Protocol 2.2
2.2.6 Unbind
An ‘unbind’ mechanism allows the bridge and HIDs to return to their default unbind mode as if they
had never bound to any system before.
The bridge dedicates a bind flag to each device type that it supports. A bind flag is a 1-bit field in
Flash. Once the bridge has been bound to an HID by either KISSBind or button bind mechanism, the
bridge sets the corresponding bind flag for that device type and stores the flag in its Flash.
If the bind flag for a particular device type is set, the bridge treats future KISSBind packets from this
device type as nonfunctional packets.
The bridge unbind process clears all bind flags, and the bridge allows devices to KISSBind.
The HID dedicates a byte in its Flash, called SIGNATURE, to indicate whether or not the HID has
bound to a bridge before. The SIGNATURE is set to 0x90 after a successful KISSBind or button
bind. If the SIGNATURE is not set to 0x90, the HID tries to KISSBind to any bridge in the area that
allows the HID to KISSBind. Once the SIGNATURE is set, the HID does not attempt to KISSBind.
Note Once the HID enters unbind mode, power-cycle the HID to exit this mode. Once the bridge is
unbound, the bridge continues to communicate with any HID that already has the bridge MID. In
order to completely unbind the system, the HIDs and bridge must be unbound.
2.2.7 Data Mode
HID
When the HID application has data to send to the bridge the HID transmits a DATA packet and lis-
tens for an AutoACK. If an AutoACK is not received, the HID retransmits the packet. If the HID does
not receive an AutoACK after N DATA_PACKETS_RETRIES of retransmissions of the data packet it
assumes the channel has become unavailable due to excessive interference and moves to recon-
nect mode.
Bridge
Data mode allows application data to be transmitted from the HID to the bridge. The bridge continu-
ously listens for data packets from the HID. When valid data is received from the HID the bridge
sends an ACK to the HID and sends the data to the USB host. If invalid data is received the bridge
ignores the packet and listens for the HID to retransmit the data. The bridge monitors the interfer-
ence level and moves to ping mode if the RSSI interference threshold RSSI_NOISE_THRESHOLD
is reached. This ensures that the bridge is operating on a clean channel.
2.2.8 Back Channel Data Support
Back channel data support provides a mechanism for the host to send data to the device at the
request of the device. The device is responsible for interrogating the bridge for back channel data
either as part of a forward data packet or a simple null packet. The device starts by setting the BCDR
bit in the data header. If the packet is successfully acknowledged by the bridge then the device
inverts the upper byte of the checksum seed and then wait for N ms before trying to receive from the
bridge for M ms. The bridge also inverts the checksum seed and wait N ms before attempting to
transmit to the device. If the bridge has more data to send then it can also set the BCDR flag and can
then expect the device to receive another packet.
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