AK8975 Datasheet, PDF (16/34 Pages) Asahi Kasei Microsystems – 3-axis Electronic Compass

[AK8975/C]
7. Serial Interface
AK8975/C 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. It is compliant with sequencial read
operation.
Data consists of Read/Write control bit (R/W), register address (7bits) and control data (8bits).
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 (7bits), and the
latter 8 bits are control data (8bits). When any of addresses listed on Table 8.1 is input, AK8975/C 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 sereal 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)
RW A6 A5 A4
A3
A2
A1 A0 D7 D6 D5 D4 D3 D2 D1
D0

SO
Hi-Z
(OUTPUT)


Figure 7.1 4-wire SPI Writing Data
MS1187-E-02
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2010/05