User's Manual Part 1

ZSTAR Sensor Board hardware overview

Wireless Sensing Triple Axis Reference design, Rev. 0.9

Freescale Semiconductor 21

3.4 ZSTAR Sensor Board hardware overview

This section describes the Sensor board in terms of the hardware design. The MC9S08QG8

microcontroller drives both the MMA7260Q sensor and the MC13191 RF transceiver.

3.4.1 Analog connections

The MMA7260Q sensor is connected to AD0, AD1, and AD2 inputs to analog-to-digital converter via RC

filters formed by R3, C3, R4, C2, R5, C1. These are recommended to minimize clock noise from the

switched capacitor filter circuit inside the sensor. Once the software filtering (also described in

3.2 A/D

conversion of XYZ levels

) is employed, these RC filters may be completely omitted.

3.4.2 g-select connections

R1, R2, R6 and R7 components are made on the PCB. R1 and R2 are just footprints with no components

assembled, while R6 and R7 are connected with copper trace allowing the user to disconnect (cut) these

lines. By default, g-sel1 and g-sel2 MMA7260Q sensor input pins (used to select the acceleration range)

are connected to pins PTB0 and PTB1 of the microcontroller. The range can be controlled by software.

If user does not want to use this feature, the g-range can be selected by placing 0R resistors in the R1

and/or R2 positions. If no resistors are assembled, MMA7260Q internal pull-down resistors will

automatically select the 1.5g range (both g-sel inputs low).

Once R6 and R7 are cut, PTB0 and PTB1 (or their alternate SCI functionality of RxD1 and TxD1, or KBI

or AD inputs) may be used. These signals are also routed to BDM connector, pins 3 and 5.

3.4.3 BDM (Background Debug Mode) connections

A J2 connector is a non-standard footprint primarily intended for in-factory programming and testing via

“spring-needle” type of connections. The J2 connector carries all standard signals for Background Debug

Mode communication so if required, one may solder wires and a standard 2x3 pins 2.54mm (100mil) pitch

header for regular BDM re-programming. The pin numbering is shown on

Figure 3-5.

Figure 3-5BDM connector layout