CP316: Microprocessor Systems and Interfacing
Introduction to the QwikFlash Development Board
To get a microcontroller operational, three subcircuits are always necessary:
power, clock, and reset. This lab investigates the clock subcircuit.
- 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.
- 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.
- 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?
- 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).
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