Applied Data Systems Bitsy Plus, User Manual, Page: 30 / 68

Bitsy Plus User’s Manual
Page 20 ADS document # 110114-1001A
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 6.2.6.
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
Ÿ
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 6.2.6.
4.3.5 Temperature Sensing
The Bitsy Plus 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 6.2.6.
4.3.6 Keypad Scan
The ADSmartIO can scan a matrix keypad up to four by five keys in size. Matrix keypads are
simpler and cost less than full keyboards and can be easily customized for your application. You
can also create a keypad matrix from a collection of normally-open switches.
When configured to scan a keypad, the ADSmartIO configures the ROWn lines as inputs with
software pull-ups enabled and configures the COLn lines as outputs set to "1"(high). For the scan,
Vref
PD1
PA4
R
tl
J3
7
5
R
th