Signal Synchronization - Aceinna IMU383 Series User Manual

IMU383 Series User's Manual
________________________________________________________________________
nSS
CLK
nSS
t
SU,NSS
CLK
MISO MSB
MOSI MSB

Signal Synchronization

The IMU383 is capable of synchronizing its output with a 1 kHz external clock signal, in the
form of a square wave, applied to Pin 2. When detected, the IMU383 ignores its internal timer,
replacing it with the external clock. Care must be taken to ensure the signal is a true 1 kHz clock
(1kHz +/-0.1%), as the firmware will assume all signals on the line have a 1 kHz frequency.
Also, once an external sync pulse is applied, the signal must remain or the unit will cease its
sampling and processing functions; the system cannot return to internal timing without resetting
the system and removing the sync signal. Note that since the output data rate of the IMU383 is
always less than the 1kHz external clock, there is a potential for ambiguity in which edge of the
1kHz clock is active (used for synchronization). Note that since the delay from the 1kHz edge to
the data ready output is ~300us, the active edge of the 1kHz clock is the one immediately
preceding the data ready pulse.
If it is desirable to determine the sensor sampling points more precisely, there are two methods of
accomplishing that. In the first method, the Sensor Sampling Indicator (pin 1) is used to detect the
sampling points (see "Method 1) below). In the second method, the Timestamp registers (read via
the Extended Burst Mode command) are used to determine the sampling points (see Method 2
below).
Note that the inertial sensors are sampled at a nominal rate of 800Hz. The sensor readings are
calibrated (at 800Hz), and decimated down to the selected Output Data Rate (ODR). The data
ready signal indicates when the latest sample has been process and is available via the SPI
interface.
Doc# 7430-1398-01
t
DELAY
Figure 12 Delay Time
t
V,MISO
bit 14 bit 13
t t
SU,MOSI h,MOSI
bit 14 bit 13
Figure 13 SPI Timing Diagram
Downloaded From
bit 1 LSB
bit 1 LSB
Oneyac.com
t
h,NSS
Page 28