1. Overview Basic PIC Circuits Development in C using CCS
Typical Tasks (A/D, PWM, timing)
How to Layout a Program
Debugging Tips
The Pumpkin protoboard

2. Basic PIC Circuits
All designs are based around the PIC16F877, a mid-range microcontroller that supports:
8kB of flash program memory
Interrupts
In-circuit programming
Hardware timers
Capture/Compare/PWM modules
10-bit A/D conversion (up to 8 channels)
Built-in USART for serial communication
Lots of Digital I/O

3. Basic PIC Circuits The most basic circuit consists of:
The microcontroller
Power and GND (+5V)
Oscillator with Caps
Typical development circuit adds:
RS232 interface (typically with a MAX2.. Chip)
LED’s / switches / etc
Schematics available on INCA web site (resources at end)

4. Programming in C Programming the PIC in C offers several advantages:
Higher level language – developer is insulated from details of the chip
Library support for common tasks (string manipulation, serial communication)
We use the CCS compiler ( which don’t suck. All examples will use CCS code

5. PIC – Common Tasks with CCS
Program Template. Starting point for just about everything
#define <16F877.h> // Define the type of chip you’re using. // Makes it easier to switch chips
#use delay(clock= ) // 20Mhz oscillator
void main() {
/* Initialization Code goes here */
while (TRUE)
/* Program Code goes here */ }

6. PIC – Common Tasks with CCS
Digital I/O
Standard I/O vs. Fast I/O
Using (standard I/O):
// Output a high on PIN_D1, low on PIN_D2
// Wait 50 us and invert
output_high(PIN_D1);
output_low(PIN_D2);
delay_us(50);
output_low(PIN_D1);
output_high(PIN_D2);

7. PIC – Common Tasks with CCS
Analog Input
Initialization:
setup_adc_ports(ALL_ANALOG);
setup_adc(ADC_CLOCK_DIV_2);
Picking a channel:
set_adc_channel(0); // Note: must wait between changing
// input channels (~ 10us)
Inputting Data:
unsigned int16 data; // Declare a 16-bit integer
data = read_adc(); // Read a 10-bit value from the // selected channel

8. PIC – Common Tasks with CCS
Using PWM
Initialization:
setup_timer_2(T2_DIV_BY_1,249,1); // Setup the PWM period
setup_ccp1(CCP_PWM); // Set CCP1 for PWM
Setting the Duty Cycle:
set_pwm1_duty(500); // See the CCS examples for the formula // for setting the PWM period and duty // cycle

9. PIC – Tips for Software Design
Design the program as a state machine
A main() loop, with:
A switch() statement that jumps to a function() which represents the actions that occur in that state
Each state function() has an output section and a transition section (which can change the current state variable)
Interrupts are very useful (for example: interrupt when data received on serial port), but can cause problems.
I.e. if you change state during an interrupt (such as an E-stop), return from the interrupt service routine, then change the state variable again (during the transition section) the interrupt change is lost.
Design with tuning and debugging in mind
Programmer time is more important than machine time – the PIC16F877 is plenty fast

10. PIC – Tips for Debugging
Use a protoboard with RS232 support and lots of print statements. Example:
program waits for a switch press
reads an analog voltage
changes the PWM cycle accordingly

11. PIC – Tips for Debugging
Some_function() {
int1 pushed = FALSE, last_pushed = FALSE;
int16 analog_value;
float volts;
pushed = input(PIN_D3);
if (pushed && !last_pushed) {
puts(“Button Pushed!”);
analog_value = read_adc(); /* 10-bit analog input value is * between V range */
volts = 5.0 * (analog_value / );
printf(“Button pushed! Analog value is %f volts, PWM to %i\n, volts, analog_value);
set_pwm1_duty(analog_value);
/* We’ve pre-configured PWM channel 1 – the set_pwm1_duty cycle function accepts
a 10-bit number and adjusts the cycle accordingly */ }

12. PIC – Tips for Debugging
Can also use conditionals to print out different types of debugging messages. Say we have a type of message, INFO that we only want to be displayed when testing certain things. We could define a MACRO:
#ifdef SHOW_INFO
#define INFO(A) puts(A);
#else
#define INFO(A) /* A */
#endif
Then, at an appropriate point in the code:
INFO(“Button Pushed”);

13. PIC – In-Circuit Programming
The PIC16F877 has on-board FLASH memory
No burner needed to reprogram the PIC
No need to remove PIC from circuit
Using a bootloader on the PIC, and a bootload utility on the PC the PIC can be reprogrammed in seconds over a serial link.
Burn the bootloader code onto the PIC
When writing your program in C tell the compiler not to use the top 255 bytes of flash memory
Connect the PIC circuit to the PC via a serial link. Run the bootloader code from the PC and download your code to the circuit in seconds
This technique is VITAL to preserving sanity

14. PIC – In-Circuit Programming
The PIC16F877 has on-board FLASH memory
No burner needed to reprogram the PIC
No need to remove PIC from circuit
Using a bootloader on the PIC, and a bootload utility on the PC the PIC can be reprogrammed in seconds over a serial link.
Burn the bootloader code onto the PIC
When writing your program in C tell the compiler not to use the top 255 bytes of flash memory
Connect the PIC circuit to the PC via a serial link. Run the bootloader code from the PC and download your code to the circuit in seconds
This technique is VITAL to preserving sanity

15. PIC – Mad2/Pumpkin PIC16F877-based Prototyping Board
PIC16F877 microcontroller with PWR/GND connected, 20Mhz oscillator
8 digital I/O points
8 LED’s (switchable to DI/O)
8 Analog Input ports (also usable as DI/O)
2 PWM channels
RS232 interface

16. Sample Application – Analog Sampling
PC Application will do the following:
Present a graphical front end to the user
Have a “sample” button that will send a character to the PIC over the serial port
Will read back a number in hex format, reformat into decimal and display on the screen
PIC Application will do the following:
Poll the serial port
If a character is received, sample analog channel 0 (A0), and print the value to the serial port as a hex number, followed by a newline/return (\r\n)
Use the value read from the analog input channel as the PWM duty cycle on channel 1

17. Mplab – Setting up for CCS
Project->New (call it main.prj)
Development Mode: Editor/16F877
Language Tool Suite: CCS
Click on main.hex, Node Properties
Click on PCM
File->New
File->Save As, main.c
Add Node, main.c
Ready to start building the application

18. Step 1: Basic Template Basic Template Code is:
Include the header file for the appropriate PIC
Note: I typically use a custom 16F877.H header file with 10-bit data acquisition turned on
Set the clock speed
Set the fuses
Set up serial communication
Reserve memory for the bootloader
Main function and debug/status message

19. Step 2: Initialize the PIC functions
Need to initialize (if using):
Analog to Digital Conversion
Counters and Timers
PWM output / capture
Interrupts
Serial
Timer
Global
Etc
I’ve included an LED test to show the card has reset

20. Step 2: Initialize the PIC functions
Need to initialize (if using):
Analog to Digital Conversion
Counters and Timers
PWM output / capture
Interrupts
Serial
Timer
Global
Etc
I’ve included an LED test to show the card has reset

21. Step 3: State Machine and Interrupts
Set up the state machine
Define the allowable states with enum’s
Define the state variables
ALWAYS INITIALIZE EVERY VARIABLE
Enter the infinite loop and check for state
Set up the interrupt handler
Serial #INT_RDA
Timer #INT_TIMER1

22. Step 3: State Machine and Interrupts
Three States
IDLE – do nothing
RECV_DATA
Enter: when serial interrupt received
Exit: when serial data handled
READ_ANALOG
Enter: when timer1 overflows (every 100 ms)
Exit: when analog data is read and PWM updated

23. Step 3: State Machine and Interrupts
The first state machine is composed with this master “on/off” state machine.
STOP: user sends a “stop” command
START: user sends a “start” command

24. Step 4: Handle ANALOG_DATA state
Declare variables to store analog input and PWM output
In the state handler:
Read in the analog voltage (remember it’s a 10-bit number, so we’ll need a 16-bit integer)
Convert to PWM rate (divide by 2, ceil to 500)
Convert to actual voltage (0-5V)
Print on the serial port
Return to IDLE state

25. Step 5: Handle Serial Input
Declare variables to store string data from the user
Copy in the get_string() function from input.c
In the state handler:
Disable interrupts
Read in a string
Check to see if it matches “start” or “stop”
Change state if necessary
Re-enable interrupts
Change state to IDLE

26. References and Links Presentation, Notes and Code Archive
CCS PIC C Compiler
CCS PIC C Compiler Manual
WorkingTex Web Site (lots of examples!)
Bootloader Code (that resides on the PIC)
Bootloader Program (that resides on the PC)