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AS3935

Datasheet - Detailed Descri p ti on

8.4 Serial Peripheral Interface (SPI)

This 4-wire standard SPI interface (Mode 1) can be used by the Microcontroller (µC) to program the AS3935. To enable the SPI as data

interface, the Select Interface (SI) has to be set to low (GND).

The maximum clock operation frequency of the SPI is 2MHz.

Note: The clock operation frequency of the SPI should NOT be identical to the resonance frequency of the antenna (500kHz), in order to

minimize the on board 500kHz noise.

Note: MISO is set to tristate if CS is high. In this way more than one device can communicate on the same MISO bus.

8.4.1 SPI Command Structure

To activate this SPI, the CS has to be set to low. A SPI command consists of two bytes serial command and the data are sampled on the falling

edge of SCLK (CPHA=1). The next table shows command structure, from the MSB (B15) to LSB (B0). The command stream has to be sent to

the SPI from the MSB (B15) to the LSB (B0).

The first two bits (B15 and B14) define the operating mode. There are two modes available – Read and Write/Direct command.

In case a write or read command happens, then the next 5 bits (B13 to B9) define the register address, which has to be written respectively read,

as shown in the table below. The direct command is performed with a write operation (see Send Direct Command Byte on page 16).

Table 10. Serial Data Interface (SDI) Pins

Name

Signal

Signal Level

Description

CS

Digital Input

CMOS

Chip Select (Active Low)

MOSI

Digital Input

CMOS

Serial data input from the external unit to the AS3935

MISO

Digital Output

CMOS

Serial data output from the AS3935 to the external unit

SCLK

Digital Input

CMOS

Clock for serial data read and write

MODE

Register Address / Direct Command

Register Data

B15

B14

B13

B12

B11

B10

B9

B8

B7

B6

B5

B4

B3

B2

B1

B0

Table 11. Bits B15, B14

B15

B14

Mode

0

0

WRITE / DIRECT COMMAND

0

1

READ

Table 12. Bits B13 to B9

B13

B12

B11

B10

B9

B8

Read / Write Register

0

0

0

0

0

0

0x00

0

0

0

0

0

1

0x01

0

0

0

0

1

0

0x02

0

0

0

0

1

1

0x03

0

0

0

1

0

0

0x04

0

0

0

1

0

1

0x05

0

0

0

1

1

0

0x06

0

0

0

1

1

1

0x07

……

…

…

…

…

…

……

…

…

…

…

…

1

1

0

0

0

1

0x31

1

1

0

0

1

0

0x32