1. Microcontroller Applications
ELEC 421
Dr. Ron Hayne
ELEC 330

2. Embedded System Typical analog/digital system Transducer A/D converter
Converts non-electrical signals into electrical signals
A/D converter
Converts analog signals into digital signals
Digital processor
Processes digital data
D/A converter
Converts digital signals into equivalent analog signals
Converts electrical signals into non-electrical signals
ELEC 421

3. Microcontroller Applications
Analog to Digital Conversion
Interface Analog Sensors (Transducers)
Pulse Width Modulation
DC Motor Control
MPLAB X IDE
Programming and Debugging
chipKIT Wi-Fire Board
PIC32 with lots of I/O
H-Bridge Motor Driver
Control Speed and Direction
ELEC 421

4. Target System for Development: PIC32MZ EF
MIPS32 Warrior M-Class processor core runs the program’s instructions
PIC32MZ microcontroller adds memory, control, interfacing and robustness circuits
chipKIT Wi-FIRE development board (REV C) adds inputs, outputs and power supply
Images courtesy of Digilent and Microchip

5. PIC32 ADC Input Support Hardware
Makes the ADC more flexible
Analog Input Voltages
Sample & Hold
Digital Output Code
ADC
Sample or hold?
Input Channel Select
Input multiplexer
Sample and hold circuit
Allows one ADC to read one of multiple inputs, reducing need for multiple ADCs
Samples input voltage before conversion
Hold last sampled voltage for conversion by ADC, reducing errors if input voltage changes

6. Basic Analog-to-Digital Conversion Process
Uses software to start conversion and detect completion
Select Channel
Trigger Conversion
Await Conversion Complete Flag
Read Data
Software
Sample & Hold
Sample
Hold
ADC
Convert
Hardware
Data Ready Status
Ready
Not ready
Conversion Result
New Result
Old result
Select analog input channel
End of conversion
Trigger ADC
ADC writes value to result register, updates conversion status flag, may generate interrupt
Sample: S&H circuit samples input voltage
Hold and convert
S&H switches to hold mode
ADC converts S&H voltage to a digital value

7. Potentiometer Connections on Wi-FIRE Board
Potentiometer wiper connected to AN8 – analog channel 8
#define VR1_AN_CHAN_NUM (8)
Ends of potentiometer resistor connected to 3.3V and 0V (ground)
Wiper will have an analog voltage from 0 to 3.3V based on its position

8. Motivation for Output Compare Module
Off
Period
Off-Time
On-Time
Enables generation of signals with precise timing
Example: Pulse-Width Modulated signal
Periodic digital signal with adjustable on-time
Duty cycle = fraction of time on, = On-Time/Period
Period = On-Time + Off-Time
Duty cycle determines average signal level
Often used for applications where slow response of user or circuit “averages out” PWM signal
Human eye averages out brightness changes which are faster than ~20 Hz (~50 ms)
So can dim a light by driving it with a PWM signal with a period under 50 ms
Also: servo motor position, electric heater control, power conversion electronics, motor speed control, …
Example: Duty Cycle 73% On
Off
10 ms
7.3 ms
2.7 ms
Average value 73%

9. Hardware Implementation: Output Compare Module
Use TMRy value to control when output OCx changes
Compare TMRy against output compare registers OCxR, OCxRS
OCxR
OCxRS
Logic
OCx
Equal
Comparator
TMRy
PRy
Comparator
Clock Input
Equal
Reset
OCxCON

10. Dual H-Bridge Motor Driver
ELEC 421

11. PICKit 3 Programmer/Debugger
ELEC 421

12. Building and Downloading Code
MPLAB X IDE
We are using the XC32 toolchain
Download Controls
xc32-as assembler
xc32-gcc C compiler
Build the files which have changed, and dependent files
xc32-g++ C++ compiler
xc32-ld linker/loader
Delete all temporary files and rebuild all files
xc32-ar archive (library) manager
Download executable to MCU flash memory
Upload executable from MCU flash memory
Debug the program

13. Running Code with the Debugger
We can download the code to the MCU and let it run
Hard to know what the program is doing and why
We will perform on-chip debugging to monitor and control the program as it runs on the MCU
Start debugging:
Debugger features
Program execution control options
Start, pause, reset program
Breakpoints: pause program if it reaches this code
Program inspection options
Variable watches
Function call stack

14. Program Execution Control Options
Exit debugger (Shift-F5)
Continue running program – run until paused or breakpoint reached (F5)
Pause program – temporarily stop program execution
Reset program – next run starts from beginning
Step over function – execute entire function, pause (F8)
Step into function – enter function, pause before executing (F7)
Run to cursor – run to code corresponding to current cursor location (F4)
Set PC at cursor – update program counter to code at cursor
Focus cursor at PC – update window to show code for current PC
PC (Program counter) value – address of next instruction to execute

15. Using Breakpoints
Use breakpoints to pause program execution at a specific point in the program
If processor tries to execute code at a breakpoint, it will pause the program and give control to the debugger
Now you can examine and change variables, step through the program to see what executes next, etc.
Set/remove breakpoints by
Left-clicking in gray column, or
Right-clicking on source code and selecting “Toggle Line Breakpoint”
Limited number of hardware breakpoints in processor (8). Need one free to single-step program execution

16. Monitoring Program Data
Variable watch window allows you to see a variable’s value (and even change it)
Also shows other information: data type, address
Can add a variable to this window by…
Right-clicking on variable name in source code window and selecting “New Watch…”
Typing in name of variable in here variable window:
Or clicking on Add Watch icon
Can see variable’s value by hovering cursor over variable name in source code

17. Microcontroller Applications
Analog to Digital Conversion
Interface Analog Sensors (Transducers)
Pulse Width Modulation
DC Motor Control
MPLAB X IDE
Programming and Debugging
chipKIT Wi-Fire Board
PIC32 with lots of I/O
H-Bridge Motor Driver
Control Speed and Direction
ELEC 421