AS3909 datasheet(25/77 Pages) AMSCO

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ams Datasheet, Confidential: 2013-Oct [3-02]

AS3909/AS3910 – 25

Appl icatio n I n f o rm a t i o n

Reading of Data from Addressable Registers (READ

Mode)

The command control Byte for a read command consists of a

command code and an address. After the command code, the

address of register to be read has to be provided from the MSB

to the LSB. Then one or more data bytes can be transferred from

the SPI slave to the master, always from the MSB to the LSB. As

in case of the write command also the read command supports

auto-incrementing address. To transfer bytes from consecutive

addresses, SPI master has to keep the SEN signal high and the

SCLK has to be active as long as data need to be read from the

slave.

SDATAI is sampled at the falling edge of SCLK (like shown in the

following diagrams), data to be read from the AS3909/10

internal register is driven to SDATAO pin on rising edge of SCLK

and is sampled by the master (μC) at the falling edge of SCLK.

A SEN LOW pulse has to be performed after register data has

been transferred in order to indicate the end of the READ

command and prepare the Interface to the next command

control Byte.

In case the register on defined address does not exist all 0 data

is sent to SDATAO. Figure 16 illustrates an example for reading

of a single byte.

Figure 16:

Reading of a Single Register Byte

Sending Direct Commands

Direct commands have no arguments, so a single byte is sent.

Command mode is entered if the SPI is started with two leading

ONE. After the COMMAND mode code 11 (see Figure 20), the

six bit command code is sent MSB to the LSB. The command is

executed on falling edge of SEN. During the direct command

execution, starting another activity over the SPI interface is not

allowed.

SEN falling

edge signals

end of READ

Mode

SCLK

raising edge

Data is moved

from Address

<A5-A0>

SCLK

falling edge

Data is

transferred

to µC

SDATAI

SCLK

SEN

SDATAO

SCLK

falling edge

Data is sampled

SCLK raising

edge data is

transferred from

µC

01 pattern indi-

cates READ

Mode

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