MRF49XAT-I-ST Datasheet, PDF (15/102 Pages) Microchip Technology – ISM Band Sub-GHz RF Transceiver

MRF49XA
2.10 Data Validity Blocks
2.10.1 RECEIVE SIGNAL STRENGTH
INDICATOR
The MRF49XA provides the RSSI signal to the host
microcontroller, and hence, supports the monitoring of
analog and digital signal strengths. A digital RSSI output
is provided to monitor the input signal level through an
internal STATUS register. The digital RSSI goes high, if
the received signal strength exceeds a given
preprogrammed RSSI threshold level. The digital RSSI
can be monitored by reading the STSREG. Alternatively,
an analog RSSI signal is also available at pin 15
(RSSIO) to determine the signal strength. The analog
RSSI settling time depends on the external filter
capacitor. Typically, a 4–10 nF capacitor provides
optimum response time for most of the applications. See
Section 4.0, Application Details and Section 5.0,
Electrical Characteristics for details on filter capacitors
for analog RSSI. The typical relationship between
analog RSSI voltage and RF input power is graphically
represented in Figure 2-2.
2.10.2 DATA QUALITY INDICATOR
The Data Quality Indicator (DQI) is a special function
which indicates the quality of the received signal and
the link. The unfiltered received data is sampled and
the number of spikes are counted in the received data
for a specified time. If the input signals are of high
value, it indicates the operating FSK transmitter of the
high output signal within the baseband filter bandwidth
from the local oscillator.
2.10.3 DATA INDICATOR OUTPUT
The Data Indicator Output (DIO) is an extension of DQI.
The DIO pin can be configured to indicate valid data
based on the actual internal settings. When an
incoming signal is detected, the DIO uses the DQI
clock recovery lock and digital RSSI signals to
determine the validity of the incoming signal. The DIO
searches for the valid data transitions at an expected
data rate. The desired data rate and the acceptance
criteria for valid data are user-programmable through
the SPI port. The DIO signal is valid when using the
internal receive FIFO or an external pin to capture
baseband data.
The DIO has three modes of operation: Slow, Medium
and Fast. Each mode is dependent on the type of
signals it uses to determine the valid data and the
number of incoming preamble bits present at the
beginning of the packet. The DIO can be multiplexed
with the INT pin for external usage.
FIGURE 2-2:
ANALOG RSSI VOLTAGE VS. RF INPUT POWER
1150
450
-100
-65
Input Power (dBm)
© 2009-2011 Microchip Technology Inc.
Preliminary
DS70590C-page 15