Eurotech BitsyXb - Adsmartio Features; Digital I;Os; Analog Inputs (A;D); Temperature Sensing

BitsyXb - User Manual
28 110118-0001A
4.3.2 ADSmartIO Features
The following are some of the functions that the ADSmartIO can perform. The functions actually
implemented depend on the firmware loaded on your system:
• General purpose digital I/O and A/D
• Keypad scan (section 4.3.6)
• PS/2 keyboard input
• Backlight on/off and brightness control (section 4.6.6)
• Contrast control for display (enabled only when pixel clock is running) (section 4.6.7)
• Read/set real-time clock (RTC) (section 4.2)
• Wakeup via /RQOnOff signal (section 5.3.3)
• Trickle-charge a battery (section 5.3.7)
• Read a temperature sensor (section 4.3.5)
• Monitor system power
• Reset CPU
4.3.3 Digital I/Os
All available ports on the ADSmartIO controller can be individually configured as inputs or
outputs. If you write a "1" to an I/O port when it is configured as an input, it enables a pull-up
resistor. Electrical specifications are listed in section 6.3.6.
4.3.4 Analog Inputs (A/D)
Each of the Port A I/Os (PA0-PA7) includes an analog-to-digital (A/D) converter. The converters
give full-scale readings when the input voltage is equal to voltage reference Vref
(e.g. V=Vrefreading/1023). Not all ports are available for external A/D use; see section 4.3.7 for
port assignments. Electrical specifications are listed in section 6.3.6.
4.3.5 Temperature Sensing
The BitsyXb ADSmartIO can read the temperature of an external
thermistor connected across pins 5 and 7 of J3. The ADSmartIO
controller drives a transistor to energize the thermistor, then reads
the result through the voltage divider created by the thermistor (R
th
)
and an internal resistor (R
tl
). The thermistor circuit is shown at
right.
Electrical specifications for the temperature sensing circuit are
listed in section 6.3.6.
Vref
PD1
PA4
R
tl
J3
7
5
R
th