Data Sheet

AC4490

Datasheet

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5.2.7 RSSI

Instantaneous

RSSI

Received Signal Strength Indicator can be used by the OEM Host as an indication of instantaneous

signal strength at the receiver. The OEM Host must calibrate RSSI without an RF signal present at

the receiver.

Calibration is accomplished by following these steps:

1. Power up only one transceiver in the coverage area.

2. Measure the RSSI to obtain the minimum value with no other signal present.

3. Power up another transceiver and begin sending data from that transceiver to the

transceiver being measured. Make sure the two transceivers are separated by

approximately ten feet.

4. Measure the peak RSSI, while the transceiver is actively receiving data from the remote

transceiver, to obtain a maximum value at full signal strength.

The following equation approximates the RSSI curve:

Signal Strength (dBm) = (-46.9 × VRSSI ) – 53.9

Figure 2: RSSI Voltage vs. Received Signal Strength

Validated RSSI

Because RSSI is only valid when the local transceiver is receiving an RF packet from a remote

transceiver, instantaneous RSSI is tricky to use. Therefore, the transceiver stores the most recent

valid RSSI value. The OEM host issues the Report Last Good RSSI command to request that

value. Additionally, validated RSSI can be obtained from Receive Packet and Send Data Complete

API commands and from the Probe command. Validated RSSI is not available at the RSSI pin.

5.2.8 UP_Reset

UP_Reset provides a direct connection to the reset pin on the AC4490 microprocessor and is used to force a soft reset.

5.2.9 CMD /Data

When CMD is held High the transceiver interprets incoming OEM Host data as transmit data to be sent to other transceivers.

When CMD Data is held Low the transceiver interprets OEM Host data as command data.

5.2.10 AD In

AD In can be used as a cost savings to replace Analog-to-Digital converter hardware. Reading of this pin can be performed

locally using the Read ADC command. See the AC4490 User Guide for command descriptions.