MRF49XA-ISLASHT datasheet(15/102 Pages) MICROCHIP

15 / 102 page

Preliminary

DS70590C-page 15

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

450

-100

-65

1150

Input Power (dBm)

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