CP316: Microprocessor Systems and Interfacing

Prelab: Introduction to the QwikFlash Development Board (power)

Objectives

To get a microcontroller operational, three subcircuits are always necessary: power, clock, and reset.  This lab investigates the power subcircuits.

Equipment

• PIC18FXX2 Data Sheet [pdf, 332pp; ©2006 Microchip Technology Inc.]
• QwikFlash board schematic

Procedure

1. To use a microcontroller, you must have power. A power supply (adapter) comes with the QwikFlash Development board. For this power supply,
   • what is the voltage?
   • is it AC or DC?
   • what is the amperage?
     
     
2. From the PIC18Fxx2 data sheet, find the pin out diagram for our microcontroller. Record the pin numbers and names of the power and ground pins (there should be 4 pins with labels V_DD and V_SS). From Section 22.0 Electrical Characteristics of the data sheet:
   • record the standard operating range for power (minimum, maximum voltage).
   • record the absolute maximum range for power (given with respect to ground).
     
     
3. On the QwikFlash board schematic, locate the microcontroller chip. Locate the microcontroller power and ground pins on the QwikFlash board schematic. You will note that there is capacitor between each power-ground pair. What is the value of the capacitor and why is it there? It is difficult to locate these capacitors on the board as components must be removed from the physical board to see the capacitors. Do not remove any components from the board.
   
   
4. Since the voltage from the power supply does not match the voltage required by the microcontroller, you must have a voltage regulator circuit. On the QwikFlash board schematic, locate the power connector, CON3, to locate the voltage regulator circuit. Sketch the circuit in your lab notebook and note the capacitor values. Locate this circuit on the physical board.
   
   
5. When the power switch is turned on, the board lights an LED to indicate power is on. Locate this circuit on the schematic and add it to the voltage regulator circuit in your lab notebook. Locate this circuit on the physical board. What is the purpose of the resistor in this circuit?
   
   Demonstration (at the lab) - explain the components involved in the power circuitry and their location in the schematic and the physical board.