PICDEM™ 2 Plus User’s Guide
DS51275B-page 12
2004 Microchip Technology Inc.
A.5
SWITCHES
Three switches provide the following functions:
• S1 – MCLR to hard reset the processor
• S2 – Active-low switch connected to RA4
• S3 – Active-low switch connected to RB0
Switches S1 and S3 have debounce capacitors, whereas S2 does not, allowing the
user to investigate debounce techniques.
When pressed, the switches are grounded. When Idle, they are pulled high (+5V).
A.6
OSCILLATOR OPTIONS
• RC oscillator (2 MHz approximately) supplied. This oscillator may be disabled by
removing jumper J7.
• Pads provided for user furnished crystal and two capacitors.
• Removable 4 MHz canned oscillator.
• 32.768 kHz (watch type) crystal for Timer1.
A.7
ANALOG INPUT
A 5 K
Ω
potentiometer is connected through a series 470 ohm resistor to AN0.
The pot can be adjusted from V
DD
to GND to provide an analog input to the parts with
an A/D module.
A.8
ICD CONNECTOR
By way of the modular connector (J5), the MPLAB ICD 2 can be connected for low-cost
debugging. The ICD connector utilizes RB6 and RB7 of the microcontroller for in-circuit
debugging.
A.9
TEMPERATURE SENSOR
This is a serial digital thermal sensor (TC74) connected to the 28 and 40-pin
microcontrollers via RC3 and RC4. Communication is accomplished with the TC74 via
it’s 2-wire I
2
C™ compatible serial port. This device has an address of
1001101b
.
A.10 SERIAL EEPROM
A 24L256 256K (32K x 8) serial EEPROM is included on the board to illustrate I
2
C bus
concepts.
A.11
LCD
An LCD display with two lines, 16 characters each, is connected to the 28 and 40-pin
sockets. There are three control lines (RA3:RA1) and four data lines (RD3:RD0).
A 5 K
Ω
pot may be installed into R20 to adjust contrast on the LCD. If this is done, R5
and R6 need to be removed.
