Data Sheet

MPU-9250 Product Specification
Document Number: PS-MPU-9250A-01
Revision: 1.0
Release Date: 01/17/2014
Allowable internal sources for generating the internal clock are:
• An internal relaxation oscillator
• Any of the X, Y, or Z gyros (MEMS oscillators with a variation of ±1% over temperature)
Selection of the source for generating the internal synchronous clock depends on the requirements for power
consumption and clock accuracy. These requirements will most likely vary by mode of operation. For
example, in one mode, where the biggest concern is power consumption, the user may wish to operate the
Digital Motion Processor of the MPU-9250 to process accelerometer data, while keeping the gyros off. In this
case, the internal relaxation oscillator is a good clock choice. However, in another mode, where the gyros
are active, selecting the gyros as the clock source provides for a more accurate clock source.
Clock accuracy is important, since timing errors directly affect the distance and angle calculations performed
by the Digital Motion Processor (and by extension, by any processor).
There are also start-up conditions to consider. When the MPU-9250 first starts up, the device uses its
internal clock until programmed to operate from another source. This allows the user, for example, to wait
for the MEMS oscillators to stabilize before they are selected as the clock source.
4.16 Sensor Data Registers
The sensor data registers contain the latest gyroscope, accelerometer, magnetometer, auxiliary sensor, and
temperature measurement data. They are read-only registers, and are accessed via the serial interface.
Data from these registers may be read anytime.
4.17 FIFO
The MPU-9250 contains a 512-byte FIFO register that is accessible via the Serial Interface. The FIFO
configuration register determines which data is written into the FIFO. Possible choices include gyro data,
accelerometer data, temperature readings, auxiliary sensor readings, and FSYNC input. A FIFO counter
keeps track of how many bytes of valid data are contained in the FIFO. The FIFO register supports burst
reads. The interrupt function may be used to determine when new data is available.
For further information regarding the FIFO, please refer to the MPU-9250 Register Map and Register
Descriptions document.
4.18 Interrupts
Interrupt functionality is configured via the Interrupt Configuration register. Items that are configurable include
the INT pin configuration, the interrupt latching and clearing method, and triggers for the interrupt. Items that
can trigger an interrupt are (1) Clock generator locked to new reference oscillator (used when switching clock
sources); (2) new data is available to be read (from the FIFO and Data registers); (3) accelerometer event
interrupts; and (4) the MPU-9250 did not receive an acknowledge from an auxiliary sensor on the secondary
I
2
C bus. The interrupt status can be read from the Interrupt Status register.
The INT pin should be connected to a pin on the host processor capable of waking that processor from
suspend.
For further information regarding interrupts, please refer to the MPU-9250 Register Map and Register
Descriptions document.
4.19 Digital-Output Temperature Sensor
An on-chip temperature sensor and ADC are used to measure the MPU-9250 die temperature. The readings
from the ADC can be read from the FIFO or the Sensor Data registers.
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