www.ams.com/LF-Receiver/AS3932

Revision 1.7

13 - 34

AS3932

Datasheet - Detailed Descr i p ti on

An on-off duty-ratio is defined. This duty ratio is programmable see R4<7:6>.

Figure 12. ON/OFF Mode

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 RTC. 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.

8.1.3 Preamble Detection / Pattern Correlation

The preamble detection and pattern correlation are only considered for the wake-up when the data correlator function is enabled (see R1<1>).

The correlator searches first for preamble frequency (constant frequency of Manchester clock defined according to bit-rate transmission, see

Table 19) and then for data pattern.

If the pattern is matched the wake-up interrupt is displayed on the WAKE output and the chip goes in Data receiving mode. If the pattern fails the

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

8.1.4 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 received

data are streamed out on the pin DAT. It is possible to put the chip back to listening mode either with a direct command (CLEAR_WAKE (see

Table 12)) or by using the timeout feature. This feature automatically sets the chip back to listening mode after a certain time R7<7:5>.

time

time

time

Channel 1

Channel 2

Channel 3

time

Presence

of carrier

t 0

t 0 + T

2* t 0

2* t 0 + T

3* t 0