33.3.3.8 KEY - Set Activation
KEY
The KEY instruction is used for communicating KEY bytes to the UPDI,
opening up for executing protected features on the device. See Table 33-5 for an overview of functions that are activated by KEYs.
For the KEY instruction, only 64-bit KEY size is supported. If the
System Information Block (SIB) field of the KEY instruction is set, the
KEY instruction returns the SIB instead of expecting incoming KEY
bytes. Maximum supported size for SIB is 128 bits.
KEY Instruction
Operation
The figure above shows the transmission of a KEY and the reception of a SIB.
In both cases, the SIZE_C field in the opcode determines the number of
frames being sent or received. There is no response after sending a KEY
to the UPDI. When requesting the SIB, data will be transmitted from the UPDI according
to the current Guard Time setting.