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Revision 6.2

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AS3931

Datasheet - Extende d O peratio n

Similar to the input shortcutting option, a 1.5 k

Ω resistor can be connected across the differential inputs when setting bit C4 to 1. This input

attenuation allows handling of very strong input signals by damping the antenna circuit. The damping depends on the Q-factor of the receiver

circuits.

10.3 WAKE Signal at the RSSI Pin

The WAKE signal, which is normally available at the WAKE pin, can be mapped to the RSSI pin additionally, which then becomes a digital output.

To do this, set the following bits:

C3 = 1 and C2 = 0 in the Channel Select Register (RSSI output mode digital)

C0 = 1 and C1 = 1 in the Channel Select Register

Note:

The RSSI pin is only active if the CS signal is active (CS = 1), otherwise RSSI is high Z.

10.4 Single WAKE Operation

The single WAKE signals of each channel can be mapped to the WAKE pin. Normally, the 3 WAKE signals are “ored” together and mapped to

the WAKE pin, so the channel with the strongest input signal will generate a WAKE signal. To map a single WAKE signal to the WAKE pin, follow

the steps:

1. Enable Test Mode: set T0 = 1 in Test Mode Register

2. Select Test Mode: set T1 = 1 and T2 = 0 in Test Mode Register

3. Select Channel: set C0 and C1 in the Channel Select Register

The single WAKE signals can also be mapped to the RSSI pin, which then becomes a digital output pin. To do this, make this step:

Select RSSI output mode digital:set C2 = 0 and C3 = 1 in the Channel Select Register

The RSSI pin is only active if the CS signal is active (CS = 1), otherwise RSSI is high Z.

It is possible to operate the WAKE pin in the normal mode first (that is all three single WAKE signals ored together) and after a wake up

detection, to use the Single WAKE mode to check which channel received the wake pattern. This must be done before clearing the WAKE pin. It

is also possible to operate the WAKE pin in normal WAKE mode and simultaneously to operate the RSSI-pin in single WAKE mode.

10.5 Using the Wake Generator

The wake generator generates artificial parasitic wakeup’s every 2 hours as a time base for an external-controlling unit to identify situations

where no true wakeup’s can be detected for a long time. For this purpose the external controlling unit must be able to distinguish between a true

wakeup (generated by one of the receiving channels) or an Artificial Wakeup. This is done by checking the receiving channels using the single

WAKE operation (see Single WAKE Operation on page 25). If a wakeup has occurred and no one of the receiving channels can be identified as

the trigger for the wake up, then the Wake Generator has triggered the wakeup. In this case, the WAKE signal has to be cleared as if a receiving

channel would have triggered the Wake Up.

Note:

The internal counter, that generates the internal wakeup by an overflow, can not be reset by clearing the wake pin or other actions.

The time between two artificial wakeups is approximately 2 hours (2h 16min 32sec); however, the first artificial wakeup generated by the Wake

Generator after activation of the feature (by setting bit T5 = 1) may come earlier then in 2:16:32 hours. This time is not defined. After the first

artificial wakeup, the time between two wake ups is then 2 hours.

The Wake Generator must be activated by programming the bit T5 = 1 in the Test Mode Register.