AS3933 datasheet(22/64 Pages) AMSCO

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[v1-08] 2015-Sep-02

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AS3933 − Detailed Description

Artificial Wake-Up

For each of these sub modes it is possible to enable a further

feature called Artificial Wake-up. The Artificial Wake-up is a

counter based on the used Clock Generator. Three bits define a

time window (see R8<2:0>). If no activity is seen within this time

window, the chip will produce an interrupt on the WAKE pin

that lasts 128

μs. With this interrupt the microcontroller (μC)

can get feedback on the surrounding environment (e.g. read

the false wake-up register R13<7:0>) and/or take actions in

order to change the setup.

Preamble Detection / Pattern Correlation

The chip can go in to this mode after detecting a LF carrier only

if the data correlation is enabled (R1<1>=1). The correlator

searches first for preamble bits and then for data pattern. The

paragraph Wake-Up Protocol: Pattern Detection Enabled

describes how the protocol can be implemented. Should the

pattern correlation be disabled (R1<1>=0), the AS3933 goes

directly in Data receiving mode (see paragraph Data Receiving).

If the received pattern matches, then the wake-up interrupt is

displayed on the WAKE output (Wake goes high) and the chip

goes in Data receiving mode. If the pattern fails, then the

internal wake-up (on all active channels) is terminated and no

interrupt is produced.

Having per default DAT_MASK disabled (R0<6>=0), the DAT pin

shows the entire demodulated incoming signal (carrier

burst+preamble+pattern+data).

If DAT_MASK is enabled (R0<6>=1), the data will be displayed

only after the generation of the WAKEUP interrupt.

Note(s): It is important to note that the Manchester decoder

must be enabled (R1<3>=1) for this feature.

Data Receiving

After a successful wake-up the chip enters the data receiving

mode. In this mode the chip can be retained a normal OOK

receiver. The data is provided on the DAT pin and in case the

Manchester decoder is enabled (see R1<3>), the recovered

clock is present on the CL_DAT. It is possible to set the chip back

to listening mode either with a direct command CLEAR_WAKE

(see Figure 29) or by using the timeout feature. This feature

automatically sets the chip back to listening mode after a

certain time defined by the bits R7<7:5>.

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