D E M O 9 S 1 2 X D T 5 1 2
J U L Y 1 8 , 2 0 0 8
15
A 0-ohm configuration resistor allows isolation of each reference voltage. Removing R10 iso-
lates VRH while removing R12 isolates VRL. Install 0805 sized 0-ohm resistors in these loca-
tions to restore the board to default configuration.
Care must be exercised when using alternate input references. The associated isolation re-
sistor must be removed before applying an alternate voltage reference or the board may be
damaged. The table below summarizes the changes necessary to use alternate VRH and/or
VRL.
Table 5: ATD Reference Voltage
Installed (Default)
Removed
R10
VRH = VDD
VRH provided by user
R12
VRL = GND
VRL provided by user
NOTE
: Damage to the board may result if an alternate reference voltage is attached without
first removing the associated configuration resistor.
USER I/O
User I/O includes 2 push button switches, one 4-position DIP switch, 4 green LEDs, a potenti-
ometer, and a Light Sensor. The sections below provide details on each User I/O. The User
option header block enables or disables each User I/O individually.
SWITCHES
The DEMO9S12XDT512 target board provides 2 push button switches and one 4-position DIP
switch for user input. Each push button switch is an active low input with a pull-up resistor bias
to prevent indeterminate input conditions. Pressing a push-button switch causes a low logic
input on the associated input.
Each DIP switch position is an active low input. Use of the DIP switches requires enabling the
associated PORTB pull-ups internal to the MCU prevent indeterminate input conditions. Mov-
ing a DIP switch position to ON causes a low logic level on the associated input. The figure
below shows the USER enable position and associated signal for each user switch.
LED’s
The DEMO9S12XDT512 target board provides 4 green LEDs for output indication. Each LED
is an active low output. A series, current-limit resistor prevents excessive diode current. Writ-
ing a low logic level to an LED output causes the associated LED to turn on. The figure below
shows the USER enable position and associated signal for each user LED.
