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CY4636 WirelessUSB™ LP Keyboard Mouse Reference Design Kit User Guide, Doc. # 001-70355 Rev. *A
A.3.4
Automatic Acknowledgment
The WirelessUSB LP radio contains an automatic acknowledgment (AutoACK) feature that allows it
to automatically send an ACK to any valid packet that is received. The WirelessUSB LP radio also
uses the concept of transactions to allow the radio in the HID to automatically power down after
transmitting a packet and receiving an AutoACK, instead of waiting for the firmware to power the
radio down. This conserves power and reduces the firmware complexity of WirelessUSB applica-
tions.
A.3.5
Network ID
The Network ID contains the parameters for the Channel Selection Algorithm as well as the PN code
to be used. HIDs retrieve the Network ID information from the bridge during the Bind Procedure. A
special Network ID is reserved for Bind Mode, known as the Bind ID. The Bind ID gives a common
channel subset so that any two devices can communicate with each other during Bind Mode. The
Network ID is composed of the following fields:
■
PIN
- This is a random number, between 2-5, that defines the Channel subset and is used in the
Channel Selection Algorithm.
■
Base Channel
- This is the first channel to be used in the Channel Selection Algorithm that deter-
mines which channels are contained in the channel subset.
■
PN Code
- This is used as an index to select one of 10 used SOP PN codes, as noted in the
radio driver.
■
CRC Seed
- This 8-bit value is used for the CRC calculation that further diversifies transmissions
from different networks. All packets sent between non-bound devices use the default CRC seed
of 0x0000. All packets sent between bound devices use a CRC seed that is common to all
devices bound to a particular bridge or network but unique from network to network.
A.3.6
Manufacturing ID
Each WirelessUSB radio contains a 4-byte Manufacturing ID (MID), that has been laser fused into
the device during manufacturing. The bridge uses its MID to help randomize channel subsets, PN
codes and Network CRC Seeds. The bridge sends its MID to the HIDs when binding. The HID then
stores the bridge's MID in non-volatile memory after binding. The HID sends the bridge's MID as part
of the Connect Request packet, allowing the bridge to verify the identity of the HID when establishing
a connection.
Both the bridge and the HID use the bridge's MID to generate the device Network ID components.
The following equations ensure that each network will have a unique set of Network ID components:
PN Code = (mid_1 << 2) + mid_2 + mid_3
Base Channel = (mid_2 >> 2) - (mid_1 << 5) + mid_3
PIN = (((mid_1 -mid_2) & PIN_MASK) + MIN_PIN)
CRC Seed = ((mid_2 >> 6)) + mid_1 + mid_3
A.3.7
Channel Selection Algorithm
The Channel Selection Algorithm produces a subset containing 13 of the possible 78 channels. The
Channel Selection Algorithm is based on the Network ID, with each channel in the subset six mega-
hertz from the nearest neighboring channels in the subset. This algorithm reduces the possibility of
multiple bridges selecting the same channels in the same order at the same time.