Rainbow Electronics AT86RF231 - Manual (Page 89)

89
8111A–AVR–05/08
AT86RF231
8.3 Received Signal Strength Indicator (RSSI)
The Received Signal Strength Indicator is characterized by:
• Minimum RSSI level is -90 dBm (RSSI_BASE_VAL)
• Dynamic range is 81 dB
• Minimum RSSI value is 0
• Maximum RSSI value is 28
8.3.1 Overview
The RSSI is a 5-bit value indicating the receive power in the selected channel, in steps of 3 dB.
No attempt is made to distinguish IEEE 802.15.4 signals from others, only the received signal
strength is evaluated. The RSSI provides the basis for an ED measurement, see
Section 8.4
“Energy Detection (ED)” on page 91 .
8.3.2 Reading RSSI
In Basic Operating Mode the RSSI value is valid in any receive state, and is updated every
t
TR25
= 2 µs to register 0x06 (PHY_RSSI).
It is not recommended to read the RSSI value when using the Extended Operating Mode. The
automatically generated ED value should be used alternatively, see
Section 8.4 “Energy Detec-
tion (ED)” on page 91 .
8.3.3 Data Interpretation
The RSSI value is a 5-bit value indicating the receive power, in steps of 3 dB and with a range of
0 -28.
An RSSI value of 0 indicates a receiver RF input power of P
RF
< -90 dBm. For an RSSI value in
the range of 1 to 28, the RF input power can be calculated as follows:
P
RF
= RSSI_BASE_VAL + 3 * (RSSI -1) [dBm]