User's Manual Part 1

Sensor Board description
Wireless Sensing Triple Axis Reference design, Rev. 0.9
20 Freescale Semiconductor
The reception window is larger to fit any incoming receive data and the current consumption is also higher
during reception, so this portion of current consumption would be one of the largest if the acknowledgment
was received in every loop cycle.
The “optional receive” feature allows huge power savings, still keeping the reception of acknowledgment
data from the data-receiving side.
Some further savings might be incorporated by utilizing the timer-triggered transceiver events that are
described in the MC13191 Reference Manual.The MC13191, for example, latches a so-called time-stamp
of each received frame. The data-receiving side may read this value and trigger the acknowledgment to
be sent at exactly specified time after reception (also, a start of data frame transmission can be
programmed as timer-triggered). The sensor board might then narrow its own receive window to perfectly
match the expected time of the acknowledgment frame. For the simplicity of code, this has not been
implemented in the current version of ZSTAR firmware.
3.3.1 MC13191 power management features
MC13191 provides several power saving modes. One of them is called Doze mode in which the
MC13191 crystal oscillator remains active. An internal timer comparator is functional too, providing a
power efficient and accurately timed way of waking-up the application after a specified time.
This feature is fully utilized within the Sensor board. The microcontroller calculates the time period for
which the application should be in power saving mode, then fills in the timer comparator registers in the
MC13191, and the microcontroller goes into Stop mode (MC13191 into Doze mode).
Once the timer reaches the pre-programmed time (a timer compare occurs), the MC13191’s IRQ signal
is asserted which brings the microcontroller out of the Stop mode. There are various scaling possibilities
that allow periods from a few µs up to 1073 seconds (~17 minutes) to be programmed, without
intervention of the microcontroller.