User Manual

ZSTAR3 Sensor Board Description
ZSTAR3 Reference Design Manual, Rev. 0.1
3-20 Freescale Semiconductor
Preliminary
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The current consumption of the transmitter is ~30mA at that time, but only for a short period of time
(typically ~600µs by 30Hz).
In order to keep the Sensor Board informed on the status of connection (for example, if the data-receiving
side - USB stick - is out of range, disconnected, etc.) and still synchronize with master, the reception has
to be turned on after the data has been transmitted. This is not really required within each loop cycle, and
in the actual implementation only on every 8
th
loop the receive window opens (receiver is enabled to
receive the acknowledgment). More in Section 5.3, “ZSTAR3 RF Protocol description.
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 MC13213 Reference Manual.The MC13213, for example, latches a so-called time-stamp
of each received frame. The data-receiving side read this value and trigger the acknowledgment sent at
exactly specified time after reception (also, a start of data frame transmission can be programmed as
timer-triggered). The Sensor Board then narrow its own receive window to perfectly match the expected
time of the acknowledgment frame.
3.2.6 MC13213 Modem Power Management Features
MC13213 modem provides several power saving modes. One of them is called Doze mode in which the
MC13213 modem 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
Modem, and the microcontroller goes into Stop mode (modem into Doze mode).
Once the timer reaches the pre-programmed time (a timer compare occurs), the modem’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.
3.3 ZSTAR Sensor Board Hardware Overview
This section describes the Sensor Board in terms of hardware design. The MC13213 SIP drives only the
analogue or digital triaxial sensor. Because for analogue and digital sensor is used only one footprint, thus
has to be connected all necassary pins for both sensors and these connection has to be logical fit for both
sensors.