MMA6525KW datasheet(42/56 Pages) FREESCALE

42 / 56 page

Sensor

Freescale Semiconductor, Inc.

MMA65xx

3.9

Serial Peripheral Interface

The device includes a Serial Peripheral Interface (SPI) to provide access to the configuration registers and digital data. Ref-

erence Section 4 for details regarding the SPI protocol and available commands.

To maximize independence between the X and Y channels, the device includes two interface blocks, one for each axis. The

X-axis interface block responds only to X-axis acceleration requests, or even addressed register commands. The Y-axis interface

block responds only to Y-axis acceleration requests, or odd addressed register commands. To the SPI master, the device oper-

ates as a single device. The internal independent blocks are transparent.

Each SPI block has an independent shift register. Once a message is received (rising edge of CS), the contents of the two

shift registers are compared. If the contents do not match, the Y-Axis SPI block will not respond, and the X-Axis SPI block will

respond with a SPI Error as shown in Table 30. If the contents match, each SPI block decodes the message, and the appropriate

block enables DO for a response during the next SPI message.

Figure 33 shows an internal diagram of the SPI.

Figure 33. SPI Diagram

Y SPI

CS_M

SCLKM

MOSIM

I/O

MISOM

SCLK

MOSI

MISO

SCLK

MOSI

MISO

SPI Master

X SPI

If Bit 13 == ‘1’

If Bit 13 = ‘0’

& Bit 14 == ‘1’

& A0 == ‘1’

If Bit 13 == ‘1’

If Bit 13 = ‘0’

& Bit 14 == ‘0’

& A0 == ‘0’

Registers

X-Axis Raw Data

X-Axis OC Data

Even Address Regs

Y-Axis Raw Data

Y-Axis OC Data

Odd Address Regs

X SPI Shift Register

Y SPI Shift Register

SPI Mismatch Error (SPI Error)

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