MRF24J40_10 Datasheet, PDF (94/156 Pages) Microchip Technology – IEEE 802.15.4™ 2.4 GHz RF Transceiver

MRF24J40
3.6 Received Signal Strength
Indicator (RSSI)/Energy Detection
(ED)
RSSI/ED are an estimate of the received signal power
within the bandwidth of an IEEE 802.15.4 channel. The
RSSI value is an 8-bit value ranging from 0-255. The
mapping between the RSSI values with the received
power level is shown in Figure 3-3 and is shown in
tabular form in Table 3-8. The number of symbols to
average can be changed by programming the
RSSINUM (TXBCON1 0x25<5:4>) bits.
The programmer can obtain the RSSI/ED value in one
of two methods.
FIGURE 3-2:
1 Octet
Frame Length
PACKET FORMAT IN RX FIFO
N Octets
Header
M Octets
Payload
3.6.1
RSSI FIRMWARE REQUEST (RSSI
MODE1)
In this mode, the host microcontroller sends a request
to calculate RSSI, then waits until it is done and then
reads the RSSI value. The steps are:
1. Set RSSIMODE1 0x3E<7> – Initiate RSSI
calculation.
2. Wait until RSSIRDY 0x3E<0> is set to ‘1’ – RSSI
calculation is complete.
3. Read RSSI 0x210<7:0> – The RSSI register
contains the averaged RSSI received power
level for 8 symbol periods.
3.6.2
APPENDED RSSI TO THE
RECEIVED PACKET (RSSI MODE 2)
The RSSI value is appended at the end of each
successfully received packet.
To enable RSSI Mode 2, set RSSIMODE2 = 1
(0x3E<6>). The RSSI value will be appended to the
RXFIFO as shown in Figure 3-2.
2 Octets
FCS
1 Octet
LQI
1 Octet
RSSI
TABLE 3-7: REGISTERS ASSOCIATED WITH RSSI/ED
Addr. Name
Bit 7
Bit 6
Bit 5
Bit 4
0x25 TXBCON1 TXBMSK WU/BCN RSSINUM1 RSSINUM0
0x3E BBREG6 RSSIMODE1 RSSIMODE2
r
r
0x210 RSSI
RSSI7
RSSI6
RSSI5
RSSI4
Bit 3
r
r
RSSI3
Bit 2
r
r
RSSI2
Bit 1
r
r
RSSI1
Bit 0
r
RSSIRDY
RSSI0
DS39776C-page 94
Preliminary
© 2010 Microchip Technology Inc.