CP316: Microprocessor Systems and Interfacing

Introduction to the QwikFlash Development Board (reset)

Objectives

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

Equipment

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

Procedure

1. The PIC18Fxx2 differentiates between eight different types of resets as listed in section 3.0 Reset of the data sheet. In the simplest cases, the system resets on
   • power up, referred to as Power-on Reset (POR),
   • external reset typically initiated from a reset switch, referred to as MCLR Reset during normal operation.
   Locate the microcontroller clear pin, MCLR, or the reset switch on the QwikFlash board schematic. Sketch the reset circuit in your lab notebook and note the resistor values. Locate this circuit on the physical board.
   
   
   
2. To ensure an internal Power-on Reset signal, the input signal must meet the V_POR (V_DD Start Voltage) and S_VDD (V_DD Rise Rate) specifications. Find these values in the electrical characteristics section, (Chapter 22), of the datasheet. Also locate the Voltage on MCLR with respect to V_SS and pay special attention to Note 2. Explain how the reset circuit works as (a) a power up reset and (b) an external reset. How is note 2 used? Explain how the V_POR (V_DD Start Voltage) is met. Show your calculations.
   
   Demonstration - explain the components involved in the reset circuitry and their location in the schematic and the physical board.