CYRF69103
Document #: 001-07611 Rev *B
Page 8 of 73
Figure 5. PMU Disabled - External Boost Converter
Low Noise Amplifier (LNA) and Received
Signal Strength Indication (RSSI)
The gain of the receiver may be controlled directly by clearing
the AGC EN bit and writing to the Low Noise Amplifier (LNA)
bit of the RX_CFG_ADR register. When the LNA bit is cleared,
the receiver gain is reduced by approximately 20 dB, allowing
accurate reception of very strong received signals (for
example when operating a receiver very close to the trans-
mitter). An additional 20 dB of receiver attenuation can be
added by setting the Attenuation (ATT) bit; this allows data
reception to be limited to devices at very short ranges.
Disabling AGC and enabling LNA is recommended unless
receiving from a device using external PA.
The RSSI register returns the relative signal strength of the
on-channel signal power.
When receiving, the device may be configured to automati-
cally measure and store the relative strength of the signal
being received as a 5-bit value. When enabled, an RSSI
reading is taken and may be read through the SPI interface.
An RSSI reading is taken automatically when the start of a
packet is detected. In addition, a new RSSI reading is taken
every time the previous reading is read from the RSSI register,
allowing the background RF energy level on any given channel
to be easily measured when RSSI is read when no signal is
being received. A new reading can occur as fast as once every
12
µs.
SPI Interface
The SPI interface between the MCU function and the radio
function is a 3-wire SPI Interface. The three pins are MOSI
(Master Out Slave In), SCK (Serial Clock), SS (Slave Select).
There is an alternate 4-wire MISO Interface that requires the
connection of two external pins. The SPI interface is controlled
by configuring the SPI Configure Register. (SPICR Addr:
0x3D).
3-Wire SPI Interface
The radio function receives a clock from the MCU function on
the SCK pin. The MOSI pin is multiplexed with the MISO pin.
Bidirectional data transfer takes place between the MCU
function and the radio function through this multiplexed MOSI
pin. When using this mode the user firmware should ensure
that the MOSI pin on the MCU function is in a high impedance
state, except when the MCU is actively transmitting data.
Firmware must also control the direction of data flow and
switch directions between MCU function and radio function by
setting the SWAP bit [Bit 7] of the SPI Configure Register. The
SS pin is asserted prior to initiating a data transfer between the
MCU function and the radio function. The IRQ function may be
optionally multiplexed with the MOSI pin; when this option is
enabled the IRQ function is not available while the SS pin is
low. When using this configuration, user firmware should
ensure that the MOSI function on MCU function is in a
high-impedance state whenever SS is high.
Figure 6. 3-Wire SPI Mode
4-Wire SPI Interface
The 4-wire SPI communications interface consists of MOSI,
MISO, SCK, and SS.
The device receives SCK from the MCU function on the SCK
pin. Data from the MCU function is shifted in on the MOSI pin.
Data to the MCU function is shifted out on the MISO pin. The
active low SS pin must be asserted for the two functions to
communicate. The IRQ function may be optionally multiplexed
with the MOSI pin; when this option is enabled the IRQ
function is not available while the SS pin is low. When using
this configuration, user firmware should ensure that the MOSI
function on MCU function is in a high-impedance state
whenever SS is high.
PRoC LP
VCC
VBat
0.047µF
0.047µF
0.047µF
0.047µF
0.047µF
10µF
6.3V
1µF
6.3V
0.047µF
1 Ohm 1%
47 Ohm
External DC-DC
Boost Converter
VDD_MICRO
VCC
0.1µF
MCU Function
P1.5/MOSI
P1.4/SCK
P1.3/nSS
MOSI
SCK
nSS
Radio Function
MOSI/MISO multiplexed
on one MOSI pin
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