
Bluegiga Technologies Oy
Page 15 of 19
5 Interfaces
5.1 Powering the Development Board
The board can be powered either from USB or from a coin cell battery. Absolute maximum battery voltage is
3.6V. USB or battery can be chosen with SW1. When switching to battery, the RS232 transceiver is disabled
because of its high current consumption. When using battery, the current measurement should also be
switched off to avoid excessive leakage current to the instrumentation amplifier U2. To minimize the leakage
currents the display, accelerometer and the potentiometer can be turned off and disconnected from the
module by SW2, SW5 and SW6.
5.2 USB
The board operates as a bus powered USB device.
5.3 RS232
The board operates as a DTE (data terminal equipment). Because of high peak currents of the RS232
transceiver, RS232 can only be used when powering the board from USB. When switching to battery the
RS232 transceiver is automatically disabled. RS232 can also be disabled and enabled by SW3. When the
RS232 transceiver is disabled all of its outputs are set to high impedance state and UART can be used
through the pin header.
5.4 Accelerometer and the Display
The accelerometer and the display share the same SPI interface. The display is selected by taking the chip
select signal low and the accelerometer is chosen by taking the chip select signal high. A charge pump
generates 3.3V supply voltage for the display.
5.5 Programming Interface
Programming interface is in J11.