MRF49XA 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 prepro-
grammed 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 incom-
ing 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 sig-
nals 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 Microchip Technology Inc.
Preliminary
DS70590B-page 13