Rainbow Electronics RF22 - Manual (Page 42)

RF22
Version: 0.1 Date: 12/23/2008
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GPIO Configuration A
30MHz
supply voltage
M
icr
ocon
tr
o
lle
r
VDD
VSS
GP1
GP2
GP3
GP4
100n
C7
100p
C8
C1
C8
L1
L3 L2
C6
C3 C2
1u
1u
VDD_RF SCLK
9
1
8
1
7
1
6
1
1
2
3
4
15
14
13
7 8 9
0
1
SDI
SDO
VDD_D RXn
TX
RFp
GPI
O
_
0
VR
_D
IG
nI
RQ
XO
UT
XI
N
nS
EL
5
VR_IF
6
AD
C_
R
E
F
GND_D
02
SD
N
11
12
C10
GP5
1u
C9
1u
L4
C4
C5
RF22
Sensor
TRSW
GPI
O
_
1
GPI
O
_
2
GPIO Configuration B
supply voltage
Mi
cr
oc
on
tr
oll
e
r
VDD
VSS
GP1
GP2
GP3
GP4
100n
C7
100p
C8
C1
C8
L1
L3 L2
C6
C3 C2
1u
1u
VDD_RF SCLK
9
1
8
1
7
1
6
1
1
2
3
4
15
14
13
7 8 9
0
1
SDI
SDO
VDD_D RXn
TX
RFp
GP
IO
_0
VR
_D
IG
nI
RQ
XOU
T
XI
N
nSE
L
5
VR_IF
6
A
DC_
REF
GND_D
02
SD
N
11
12
C10
GP5
1u
C9
1u
L4
C4
C5
RF22
Data CLK
Data Input/Output
Micrcontroller CLK
30MHz
GP
IO
_1
GP
IO
_2
8.9. Antenna-Diversity
To mitigate the problem of frequency-selective fading due to multi-path propagation, some transceiver systems use a
scheme known as Antenna Diversity. In this scheme, two antennas are used. Each time the transceiver enters RX
mode the receive signal strength from each antenna is evaluated. This evaluation process takes place during the
preamble portion of the packet. The antenna with the strongest received signal is then used for the remainder of that
RX packet. The same antenna will also be used for the next corresponding TX packet.
This chip fully supports Antenna Diversity with an integrated Antenna Diversity Control Algorithm. By setting
GPIOx[4:0]=10111 and 11000, the required signal needed to control an external SPDT RF switch (such as PIN diode
or GaAs switch) is made available on the GPIOx pins. The operation of these switches is programmable to allow for
different Antenna Diversity architectures and configurations. The antdiv[2:0] register is found in register 08h. The GPIO
pin is capable of sourcing up to 5 mA of current, so it may be used directly to forward-bias a PIN diode if desired.
When the arrival of the packet is unknown by the receiver the antenna diversity algorithm (antdiv[2:0] = 100 or 101) will
detect both packet arrival and selects the antenna with the strongest signal. The recommended preamble length to