Silicon Laboratories Si4010 User Manual page 4

Si4010-Keyfob-AES-DEMO
3.3. Button is Pressed on the Key Fob
If any single button or button combination (except association combination) is pressed on the key fob, then it
transmits a key fob data packet showing the button number in the button field.
Table 3. The MAC Payload Field of the "Key Fob Data" Packet
NHDR
1 byte 1 byte
0x04 AES
3.3.1. Meaning of the Different Fields
 AES—Defines whether the transmitter is using AES-128 encryption. It is set to 0x01, then Button, Temp,
Battery, and Rolling counter fields of the packets are extended to 16 bytes length all together and are encoded
by AES-128. Other fields of the packet are not affected by the encryption.
 Address—4 bytes of key fob address. The four-byte random number factory burned in the Si4010 is used as
the address.
 Button—Each bit of this byte corresponds to the status of a push button on the key fob. If the bit is set, the
given button is pressed. If the bit is cleared, the button is released.
 TEMP—The temperature is encoded as a signed 16-bit integer. Each incremental bit of temperature reading
represents 0.1 °C. If the temperature function is not implemented in the key fob, this field is set to 0xFFFF.
 Battery—1 byte unsigned char showing the actual power supply status of the key fob. It must be interpreted as
follows:
1 bit
Lbd Available
 LBD Available Bit—If set, the LBD status bit shows the actual status of the battery.
 LBD Status—Shows whether the actual battery voltage is above the LBD limit (set if the actual voltage is below
the threshold). The LBD limit is configurable in the key fob program.
 Battery Voltage Available—If set, the battery voltage information is available.
 Battery Voltage—It shows the actual battery voltage of the key fob. Each increment of the battery voltage bit
corresponds to 50 mV. However, 0 represents 1.7 V.
 Rolling Counter—The transmitter increments a 4 byte counter after every packet transmission. This counter is
stored in the MTP memory of the Si4010.
Since AES is used by the key fob, the receiver board decrypts the encrypted portion of the packet and discards the
dummy bytes. Then, the receiver board checks the sync counter value against its own copy of the sender key fob's
counter. If the key fob sync counter value minus the copy counter value is more than zero and less than a
configurable window value (default value is 10), the master increments the copy.
4
MAC Payload
4 bytes 1 byte
Address Button
1 bit
LBD Status
Rev 1.1
NWK payload
2 bytes 1 byte
TEMP Battery
1 bit
Battery Voltage Available
4 byte
Rolling Counter
5 bits
Battery Voltage[4:0]