User Manual

ZSTAR Sensor Board hardware overview
Wireless Sensing Triple Axis Reference design, Rev. 0.9
Freescale Semiconductor 23
3.4.5 Button connections
Two buttons (S1 and S2) are connected directly to pins PTB6 and PTB7. Both have internal pull-up
resistors, but are not part of the Keyboard interrupt module, therefore don’t allow a direct microcontroller
wake-up from the Stop modes.
3.4.6 MC13191 to MC9S08QG8 microcontroller interface
In order to fit all the necessary circuitry onto a 16-pin microcontroller, the full recommended MC13191
interface has had to be reduced. The full interface includes the following connections:
• 4-wire Synchronous Peripheral Interface (SPI) connection (MISO, MOSI, SPICLK, CE
)
• Interrupt Request signal (IRQ
)
• Attention (ATTN
) wake-up signal
• Receive/Transmit Enable (RXTXEN) signal
• External Reset (RST
) signal
SPI and IRQ
are vital for the communication and configuration ofthe MC13191. SPI is connected to the
MC9S08QG8 SPI module (pins PTB4/MISO1, PTB3/MOSI1, PTB2/SPSCK1, and GPIO pin PTB5 for
CE
).
Interrupt Request (IRQ
) is connected to the microcontroller IRQ pin sharing its alternate RESET function
when BDM communication is active.
Attention (ATTN
) signal is intended to externally wake-up the MC13191 from Doze and Hibernate
modes. Since this feature is not used and exit from the Doze mode is done using a timer compare event,
The ATTN
pin is not routed to the microcontroller and needs to be connected to V
dd
.
Receive/Transmit Enable (RXTXEN) signal is used to control transitions to/from receive and transmit
modes. Since this can be accomplished just by software programming and/or timer compare events, this
connection to the microcontroller may also be omitted, saving an additional pin. RXTXEN is connected to
V
dd
.
External Reset (RST
) signal places the transceiver in a complete reset condition (Off mode and power
down). Alternative Software reset is also possible and since Off mode (the one with the lowest possible
power consumption) is not required too, RST
is connected to V
dd
too.
3.4.7 MC13191 RF interface
The RF interface (antennas) were designed with the cost and board size in mind. Among several designs,
the PCB layout antennas were in the main consideration (cost). Of several PCB antenna designs
available for the 2.4GHz band (F-antenna, dipole, loop), the loop antenna has been selected mainly
because of the size required on the PCB.
The MC13191 transceiver is designed with separated RF IN (receive) and PA OUT (transmit) paths. To
avoid the need for an antenna switch, two separate antennas need to be used. Both ZSTAR boards (USB
stick and Sensor Board) use the same antenna layout, there are two antennas on the PCB, just on the
opposite sides of the PCB.
The antenna is designed as a rectangle, 20x24mm (780x940mils), made of 1.25mm (50mils) wide trace
of copper. The corners are rounded with a 3.8mm (150mils) radius.