User Manual

136
8111A–AVR–05/08
AT86RF231
11.2 Random Number Generator
11.2.1 Overview
The AT86RF231 incorporates a 2-bit truly random number generator by observation of noise.
This random number can be used to:
he random number is updated every T
TR29
= 1 µs in Basic Operation Mode receive states. The
values are stored in register bits RND_VALUE (register 0x06, PHY_RSSI).
11.2.2 Register Description
Register 0x06 (PHY_RSSI):
Register 0x06 (PHY_RSSI) is a multi purpose register to indicate FCS validity, to provide ran-
dom numbers and an RSSI value.
• Bit 7 - RX_CRC_VALID
Refer to register description in Section 8.2.5 “Register Description” on page 87.
• Bit [6:5] - RND_VALUE
The 2-bit random value can be retrieved by reading register bits RND_VALUE. Note that the
radio transceiver shall be in Basic Operating Mode receive state. The values are updated each
T
TR29
=1µs.
• Bit [4:0] - RSSI
Refer to register description in Section 8.3.4 “Register Description” on page 90.
• Generate random seeds for CSMA-CA algorithm
see Section 7.2
• Generate random values for AES key generation
see Section 11.1
Bit 7 6 5 43210
+0x06 RX_CRC_VALID RND_VALUE RSSI PHY_RSSI
Read/Write R R R RRRRR
Reset Value 0 0 0 0 0 0 0 0