PNI SENtral MandM - Manual (Page 13)

PNI Sensor Corporation Doc #1020129 revE
SENtral M&M Technical Datasheet Page 12
3.3 I
2
C Sensor Interface (Sensor Bus)
Understanding how the sensor interface operates is not necessary when using the SENtral
M&M module. However, understanding the sensor interface is useful if there is a need to
communicate directly with a sensor or the EEPROM in Pass-Through state.
The SENtral Motion Coprocessor on the SENtral M&M module communicates with the
module’s accelerometer, gyroscope, and magnetometer over the module’s sensor bus, where
SENtral is the I
2
C master and the sensors are slave devices. On the sensor bus, SENtral
initiates data transfer and generates the serial clock. The two wires comprising the sensor
bus are SDAM, the serial data line, and SCLM, the serial clock. Both are bidirectional and
driven by open drain transistors within SENtral. These can be monitored by the host, but
should not be written to by the host. Each line is attached to a 4.7 kΩ pull-up resistor.
SENtral’s I
2
C sensor interface supports Standard mode with a rate up to 100 kbit/s, Fast
mode with a rate up to 400 kbit/s, and Fast Plus mode with a rate up to 1000 kbit/s.
3.4 Host Interrupt/GPIO Lines
GPIO[6] provides an interrupt to the host whenever a defined event occurs. Exactly which
types of events will trigger an interrupt are set by the EnableEvents register, which is
discussed in Section 4.2 This interrupt line can be used to signal the host that new results are
available for reading. Alternately, the host may poll SENtral’s EventStatus register,
discussed in Section 0, to determine if any events of interest have been updated. If polling will be
used, PNI recommends polling on a regular interval such that an error event will be identified in a
timely manner.
GPIO[4] is not currently used, and generally should be left unconnected. This is also true for
GPIO[3] and GPIO[5], which are only accessible on the SENtral White M&M.