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AS3935

Datasheet - Detailed Descri p ti on

8.5.2 I²C Register Read

To read data from the slave device, the master has to change the transfer direction. This can be done either with a repeated START condition

followed by the device-read address, or simply with a new transmission START followed by the device-read address, when the bus is in IDLE

state. The device-read address is always followed by the 1st register byte transmitted from the slave. In Read Mode, any number of subsequent

register bytes can be read from the slave. The word address is incremented internally.

Figure 19. I²C Page Read

Random Read and Sequential Read are combined formats. The repeated START condition is used to change the direction after the data transfer

from the master.

The word address transfer is initiated with a START condition issued by the master while the bus is idle. The START condition is followed by the

device-write address and the word address.

In order to change the data direction, a repeated START condition is issued on the 1st CLK pulse after the ACKNOWLEDGE bit of the word

address transfer. After the reception of the device-read address, the slave becomes the transmitter. In this state, the slave transmits register data

located by the previous received word address vector. The master responds to the data byte with a NOT ACKNOWLEDGE, and issues a STOP

condition on the bus.

In contrast to the Random Read, in a sequential read the transferred register-data bytes are responded by an acknowledge from the master. The

number of data bytes transferred in one sequence is unlimited (consider the behavior of the word-address counter). To terminate the

transmission, the master has to send a NOT ACKNOWLEDGE following the last data byte and subsequently generate the STOP condition.

8.5.3 Direct Command

It is possible to send direct commands writing 0x96 in the registers REG0x3C and REG0x3D, as shown in the table below:

8.6 Voltage Regulator

The AS3935 can be either supplied by a voltage regulator or directly.

If the voltage regulator is used, an additional current consumption (around 5µA) will have to be considered. In this case the pin EN_VREG must

be connected to VDD and the AS3935 is supplied by the pin VDD, while the regulated voltage is at the pin VREG (output of the voltage

regulator). In order to fulfil the stability requirements of the voltage regulator a capacitance greater than 1µF on the pin VREG to ground is

needed. The nominal output regulated voltage is 3V.

If the voltage regulator is not used, the pin EN_VREG must be connected to ground and the pins VDD and VREG must be connected together to

the supply voltage (e.g. battery).

Direct Command

Register

PRESET_DEFAULT

0x3C

CALIB_RCO

0x3D

S

DW

A

WA

A

DR

P

A

Data 1

AAA

Data 2

A

…...

A

WA++

WA++

WA++

Sr

Data n

N

Slave (AS3935) as transmitter

Slave (AS3935) as receiver