Freescale Semiconductor
15
USER I/O
User I/O includes 2 push button switches, one 4-position DIP switch, 4 green LEDs, a
potentiometer, and a photo-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 APS12DT256SLK 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.
Moving a DIP switch position to ON causes a low logic level on the associated input. Table 4
shows the associated connection signal for each switch. Table 5 shows the associated USER
enable position to enable each switch.
LED’s
The APS12DT256SLK target board provides 4 green LEDs for output indication. Each LED is
an active low output. A current-limit resistor prevents excessive diode current. Writing a low
logic level to an LED output causes the associated LED to turn on. Table 4 shows the
associated connection signal for each LED. Table 5 shows the associated USER enable
position to enable each LED.
POT
A single-turn, 3/8 inch, 5K ohm trimmer potentiometer (POT) has been provided as user,
analog input. The part is decoupled to minimize noise during adjustment. The POT connects
to analog input PAD05/AN05 on the MCU. Table 4 shows the associated connection signal for
the POT. Table 5 shows the associated USER enable position to enable the POT.
Photo-Sensor
A 4mm photocell light sensor exhibiting 23K – 33K ohms of output resistance has been
provided. Output resistance is inversely related to incident light intensity. A gain stage (U5)
amplifies the sensor output before connecting to the MCU. The SENSOR connects to analog
input PAD04/AN04 on the MCU. Table 4 shows the associated signal connection for the
sensor. Table 5 shows the associated USER enable position to enable the sensor.
