si4430 Silicon Laboratories, si4430 Datasheet - Page 66

• Manufacturer Part Number: si4430
• Description: Si4430 Ism Transceiver
• Manufacturer: Silicon Laboratories

Si4430
8.10. RSSI and Clear Channel Assessment
The RSSI (Received Signal Strength Indicator) signal is an estimate of the signal strength in the channel to which
the receiver is tuned. The RSSI value can be read from an 8-bit register with 0.5 dB resolution per bit. Figure 30
demonstrates the relationship between input power level and RSSI value. The RSSI may be read at anytime, but
an incorrect error may rarely occur. The RSSI value may be incorrect if read during the update period. The update
period is approximately 10 ns every 4 Tb. For 10 kbps, this would result in a 1 in 40,000 probability that the RSSI
may be read incorrectly. This probability is extremely low, but to avoid this, one of the following options is
recommended: majority polling, reading the RSSI value within 1 Tb of the RSSI interrupt, or using the RSSI
threshold described in the next paragraph for Clear Channel Assessment.
For Clear Channel Assessment a threshold is programmed into rssith[7:0] in "Register 27h. RSSI Threshold for
Clear Channel Indicator". After the RSSI is evaluated in the preamble, a decision is made if the signal strength on
this channel is above or below the threshold. If the signal strength is above the programmed threshold then a 1 will
be shown in the RSSI status bit in "Register 02h. Device Status", "Register 04h. Interrupt/Status 2", or configurable
GPIO (GPIOx[3:0] = 1110).
66
Add R/W
26
27
R/W
R
250
200
150
100
50
RSSI Threshold for Clear Channel Indicator
0
-120
Received Signal Strength Indicator
Function/Description
-100
Figure 30. RSSI Value vs. Input Power
-80
rssith[7]
RSSI vs Input Power
rssi[7]
D7
Preliminary Rev. 0.4
-60
rssith[6]
rssi[6]
In Pow [dBm]
D6
rssith[5]
rssi[5]
D5
-40
rssith[4]
rssi[4]
D4
rssith[3]
rssi[3]
D3
-20
rssith[2]
rssi[2]
D2
rssith[1]
rssi[1]
0
D1
rssith[0]
rssi[0]
D0
20
POR Def.
00h
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