AN4650 datasheet(55/102 Pages) STMICROELECTRONICS

55 / 102 page

DocID027415 Rev 1

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AN4650

Android embedded functions

102

When the maximum value 16777215 LSB (corresponding to FFFFFFh) is reached and low

resolution (TIMER_HR = 0) is used, the counter is automatically reset to 000000h and

continues to count. When the maximum value is reached and high resolution (TIMER_HR =

1) is used, the counter is not automatically reset to 0 and freezes at FFFFFFh. In any case,

the timer count can be reset to zero at any time by writing the reset value AAh in the

TIMESTAMP_REG2 register.

An interrupt signal is generated when the timer step count reaches the value of 16776960

LSB (corresponding to FFFF00h). This interrupt signal can be driven to the INT1 pin by

setting to 1 the INT1_TIMER bit of the MD1_CFG register. Once the interrupt pin is

asserted, it must be reset to zero by writing AAh in the TIMESTAMP_REG2 register.

The time stamp count can be stored in FIFO as a fourth data set along with the step counter

data (see Section 8.9 for details).

A basic SW routine to enable the time stamp counter is shown below.

Write 50h into CTRL1_XL

// Turn on the accelerometer

// ODR_XL = 208 Hz, FS_XL = 2g

Write 80h into TAP_CFG

// Enable time stamp count

Write 10h into WAKE_UP_DUR

// Time stamp resolution = 25us

Write 01h into MD1_CFG

// End counter interrupt driven to INT1 pin

AN4650 Datasheet(PDF) 55 Page - STMicroelectronics