AK09912 Datasheet, PDF (22/42 Pages) HuaXinAn Electronics CO.,LTD – 3-axis Electronic Compass

7. Serial Interface
[AK09912]
AK09912 supports I²C bus interface and 4-wire SPI. A selection is made by CSB pin. When used as 3-wire SPI, set SI pin
and SO pin wired-OR externally.
CSB pin=“L”:
4-wire SPI
CSB pin=“H”:
I2C bus interface
7.1. 4-wire SPI
The 4-wire SPI consists of four digital signal lines: SK, SI, SO, and CSB, and is provided in 16bit protocol. Data consists of
Read/Write control bit (R/W), register address (7-bit) and control data (8-bit). To read out all axes measurement data (X, Y,
Z), an option to read out more than one byte data using automatic increment command is available. (Sequential read
operation)
CSB pin is low active. Input data is taken in on the rising edge of SK pin, and output data is changed on the falling edge of
SK pin. (SPI-mode3)
Communication starts when CSB pin transits to “L” and stops when CSB pin transits to “H”. SK pin must be “H” during
CSB pin is in transition. Also, it is prohibited to change SI pin during CSB pin is “H” and SK pin is “H”.
7.1.1. Writing Data
Input 16 bits data on SI pin in synchronous with the 16-bit serial clock input on SK pin. Out of 16 bits input data, the first 8
bits specify the R/W control bit (R/W=“0” when writing) and register address (7-bit), and the latter 8 bits are control data
(8-bit). When any of addresses listed on Table 8.1 is input, AK09912 recognizes that it is selected and takes in latter 8 bits
as setting data.
If the number of clock pulses is less than 16, no data is written. If the number of clock pulses is more than 16, data after the
16th clock pulse on SI pin are ignored.
It is not compliant with serial write operation for multiple addresses.
CSB
SK
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
SI
(INPUT)
SO
(OUTPUT)
RW A6 A5 A4 A3 A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0
6
Hi-Z
Figure 7.1 4-wite SPI Writing Data
MS1547-E-02
- 22 -
2014/7