CY4636 WirelessUSB™ LP Keyboard Mouse Reference Design Kit User Guide, Doc. # 001-70355 Rev. *A
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A.3.13.2
Encryption and Power Consumption Trade Off
If the keyboard encryption is enabled, each key code is encrypted into an 8 byte key code (the Keep
Alive and key up packets are not encrypted). When a single key is pressed, a non-encrypted key
down packet consists of 16-bit Pr 2 bytes SOF + 1 byte packet 1 byte key code +
2 bytes CRC while an encrypted key down packet consists of the same overhead packets plus 8
byte key code instead of 1 byte key code. As a result, the active transmit Icc increases by approxi-
mately 50%. This results in an increase in the average power consumption when encryption is
enabled. The measurement shows that the average Icc in test mode is 3.33 mA if encryption is dis-
abled. If encryption is enabled, the average Icc increases to 3.66 mA.
Figure A-14. Encryption Key Management