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AS3931

Datasheet - Detailed Descr i pti on

8.3 Basic Operation

8.3.1 LF Transmission Protocol

8.3.1.1 Data Pattern

The AS3931 identifies a 16 half-bit binary coded data pattern, which is ASK-modulated on a LF carrier. The pattern must contain 8 LOGIC 0 half-

bits and 8 LOGIC 1 half-bits in order to be DC free. Furthermore, for a proper detector threshold adaptation it has to be ensured that there are no

long groups of LOGIC 0 and LOGIC 1 half-bits. Therefore coding of the 16 half-bit binary data to 8 Manchester bits is common. This means that

8 consecutive half-bit pairs are grouped to Manchester bits whereas a Manchester bit 1 is a HIGH to LOW transition and a Manchester bit 0 is a

LOW to HIGH transition. The AS3931 supports the Manchester bit pattern 96 [hex] which in binary code is: 10 01 01 10 01 10 10 01. MSB is

transmitted first. The Manchester bit pattern i.e. the binary DATA pattern can be changed on demand by a metal mask modification.

8.3.1.2 Double Data Pattern

To increase the immunity against parasitic wakeups, the data pattern necessary for a successful wakeup can be doubled by programming the

AS3931: if the double data pattern is used, the pattern 96 has to be sent twice; after recognition of the first data pattern, the second data pattern

has to be sent immediately after the first one, otherwise no WAKE signal is generated. For the timing see Wake Up Frame on page 15. Setting

the bit M1 to 1 can program the double data pattern feature.

8.3.1.3 Wake Up Frame

The Wake Up Frame of AS3931 consists of a preamble used for detector threshold adaptation followed by the DATA pattern once (normal or

single Wake Up) or twice (double Wake Up) to be identified. We recommend a transmission protocol as shown on Figure 15 and Figure 16. The

half-bits (according to 4 manchester bits “1”).

Figure 15. Wake Up Frame of AS3931 with Single WAKE Data Pattern

Figure 16. Wake Up Frame of AS3931 with Double WAKE Data Pattern

Preamble

Data 96

5.86 ms (16 half-bits)

WAKE

LF Carrier

Amplitude

Preamble

N

Data 96

5.86 ms (16 half

-bits)

WAKE

LF Carrier

Amplitude

Data 96

5.86 ms (16 half-bits)