CP316: Microprocessor Systems and Interfacing

Introduction to the QwikFlash Development Board (clock)

Objectives

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

Equipment

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

Procedure

1. Every microcontroller needs a clock circuit; typically composed of two capacitors and a crystal. The clock determines the speed at which the instructions are executed. From the PIC18Fxx2 data sheet, record the pin numbers and names of the clock in and clock out pins (2). On the QwikFlash board schematic, locate these pins to locate the clock or oscillator circuit. Sketch the circuit in your lab notebook and note the capacitor and crystal values. Locate this circuit on the physical board.
   
   
2. The PIC18Fxx2 can be operated in eight different oscillator modes. Use section 2.0 Oscillator Configurations of the PIC18Fxx2 data sheet to determine which oscillator modes are valid for the QwikFlash board.  Hint: Start by eliminating all oscillator modes that are not based on a crystal and then look at the crystal value.
   
   
3. You need to know the oscillator mode because this is one of the configurable parameters.  What is the oscillator mode configuration in led_delay.asm?
   
   
4. The PIC18Fxx2 devices include a feature that allows the system clock source to be switched from the main oscillator to an alternate low frequency clock source. In the oscillator configuration section there is a subsection on the oscillator switching feature. Which pins will be used for the alternate clock source (names, pin numbers)? Locate these pins on the QwikFlash board schematic. For the QwikFlash board, do you have access to these pins to implement the alternate clock source?
   
   
   Demonstration - explain the components involved in the clock circuitry and their location in the schematic and the physical board. Be prepared to explain how you determined the oscillator mode (question 2) and how it was configured (question 3).