AS3911 datasheet(55/149 Pages) AMSCO

55 / 149 page

ams Datasheet, Confidential: 2013-Oct [2-03]

AS3911 – 55

Appl icatio n I n f o rm a t i o n

The direct command Unmask Receive Data is enabling normal

processing of the received data (signal rx_on is set high to

enable the RSSI and AGC operation), the receive data framing

block is enabled. A common use of this command is to enable

again the receiver operation after it was masked by the

command Mask Receive Data. In case Mask Receive Timer is

running while command Unmask Receive Data is received,

reception is enabled, Mask Receive Timer is reset.

The commands Mask Receive Data and Unmask Receive Data

are only accepted when the Receiver is enabled (bit rx_en is set).

Direct command chaining is possible.

IRQ due to termination of direct command is not produced.

Measure Amplitude

This command measures the amplitude on the RFI inputs and

stores result in the A/D Converter Output Register.

When this command is executed the Transmitter and Amplitude

Detector are enabled, the output of the Amplitude Detector is

multiplexed to the A/D Converter input (the A/D Converter is

in absolute mode). The Amplitude Detector conversion gain is

0.6 VINPP/ VOUT. One LSB of the A/D converter output represents

13.02 mVpp on the RFI inputs. A 3 Vpp signal, which is maximum

allowed level on each of the two RFI inputs, results in 1.8 V

output DC voltage and would produce a value of 1110 0110b

on the A/D converter output.

Duration time: 25 μs max.

This command is accepted in case en (bit 7 of the Operation

Control Register) is set and Xtal oscillator frequency is stable.

Direct command chaining is not possible.

IRQ due to termination of direct command is produced after

command execution is terminated.

Squelch

This direct command is intended to avoid demodulation

problems of transponders which produce a lot of noise during

data processing. It can also be used in a noisy environment. The

operation of this command is explained in “Squelch” on

page 22.

Duration time: 500 μs max.

This command is only accepted when the Transmitter and the

Receiver are operating. Command is actually executed only in

case signal rx_on is low.

Direct command chaining is not possible.

IRQ due to termination of direct command is not produced.

Reset Rx Gain

This command initializes the AGC, Squelch and RSSI block.

Sending this command stops a squelch process in case it is

going on, clears the current Squelch setting and loads the

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