Data Sheet

ICM-20948
Document Number: DS-000189 Page 25 of 89
Revision: 1.3
The self-test response for each gyroscope axis is defined in the gyroscope specification table, while that for each
accelerometer axis is defined in the accelerometer specification table.
When the value of the self-test response is within the specified min/max limits, the part has passed self-test. When
the self-test response exceeds the min/max values, the part is deemed to have failed self-test. It is recommended to
use InvenSense MotionApps software for executing self-test.
4.14 CLOCKING
The internal system clock sources include: (1) an internal relaxation oscillator, and (2) a PLL with MEMS gyroscope
oscillator as the reference clock. With the recommended clock selection setting (CLKSEL = 1), the best clock source for
optimum sensor performance and power consumption will be automatically selected based on the power mode.
Specifically, the internal relaxation oscillator will be selected when operating in accelerometer only mode, while the
PLL will be selected whenever gyroscope is on, which includes gyroscope and 6-axis modes.
As clock accuracy is critical to the preciseness of distance and angle calculations performed by DMP, it should be noted
that the internal relaxation oscillator and PLL show different performances in some aspects. The internal relaxation
oscillator is trimmed to have a consistent operating frequency at room temperature, while the PLL clock frequency
varies from part to part. The PLL frequency deviation from the nominal value in percentage is captured in register
TIMEBASE_CORRECTION_PLL (detailed in section 12.5), and users can factor it in during distance and angle
calculations to not sacrifice accuracy. Other than that, PLL has better frequency stability and lower frequency variation
over temperature than the internal relaxation oscillator.
4.15 SENSOR DATA REGISTERS
The sensor data registers contain the latest gyro, accelerometer, 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.
4.16 FIFO
The ICM-20948 contains a FIFO of size 512 bytes (FIFO size will vary depending on DMP feature-set) 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 Section 7.
4.17 FSYNC
The FSYNC pin can be used from an external interrupt source to wake up the device from sleep. It is particularly useful
in EIS applications to synchronize the gyroscope ODR with external inputs from an imaging sensor. Connecting the
VSYNC or HSYNC pin of the image sensor subsystem to FSYNC on ICM-20948 allows timing synchronization between
the two otherwise unconnected subsystems.
An FSYNC_ODR delay time register is used to capture the delay between an FSYNC pulse and the very next gyroscope
data ready pulse.
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. Section 5 provides a
summary of interrupt sources. The interrupt status can be read from the Interrupt Status register.
For further information regarding interrupts, please refer to Section 7.