Introduction to Embedded C Programming with PIC18

Chapter 1

Objectives

• Upon completion of this chapter, you will be able to:– Examine C data types for the PIC18– Program C code for time delay – Program C code for I/O operations– Program C code for logic and arithmetic

operations

Why program the PIC18 in C?

• It is easier and less time consuming• C is easier to modify and update• Easily import code available in function

libraries (i.e. delays, uart, adc, etc.)• C code is portable to other microcontroller

with little or no modification (ANSI C format)

• We will be using Microchip C18 compiler

C data types for the PIC18

-32768 to +3276716-bitint

0 to 6553516-bitunsigned int

-128 to +1278-bitchar

0 to 2558-bitunsigned char

Data RangeBit SizeData Type

*PIC18 has a limited number of registers and data RAM locations

Example 1Write a C program to send values 00 – FF to Port B

Time Delay

• Three ways to create time delay in PIC18:– Using simple loop– Using delay function library– Using the PIC18 timers

Example 2Write a C program to toggle all the bits of PORTB (simple loop)

delays.h Function Library

Inserts 20,000 instruction cycles (number must be between 0 and 255) (0 causes a delay of 2,560,000)

Delay10KTCYx(20);Delay10KTCYx

Inserts 3000 instruction cycles (number must be between 0 and 255) (0 causes a delay of 256,000)

Delay1KTCYx(3);Delay1KTCYx

Inserts 1000 instruction cycles (number must be between 0 and 255) (0 causes a delay of 25,600)

Delay100TCYx(10);Delay100TCYx

Inserts 100 instruction cycles (number must be between 0 and 255) (0 causes a delay of causes 2560)

Delay10TCYx(10);Delay10TCYx

Inserts a single NOP instruction into the program

Delay1TCY();Delay1TCY

NoteExampleFunction

*All the related libraries can be found in the MPLAB C18 Libraries

Example 3Write a C program to toggle all the bits of PORTB (delay function library)

Time Delays using the delays.h• To determine the time generated by the delays.h

functions use the following equation.

4Clock Frequency

• If the clock frequency is 4 MHz then the instruction time is 1.0 μs so if a Delay10TCYx(8) is used in a program it causes an 80 μs time delay.

= instruction time, TCY

I/O Programming in C (Exercise 1)

Write a C program to get a byte of data from PORTB, wait 0.5 second, and then send it to PORTC. Assume XTAL = 4MHz.

Exercise 1 Solution Write a C program to get a byte of data from PORTB, wait 0.5 second, and then send it to PORTC. Assume XTAL = 4MHz.

I/O Programming in C (Exercise 2)

Write a C program to get a byte from PORTC. If it is less than 100, send it to PORTB; otherwise, send it to PORTD

Exercise 2 SolutionWrite a C program to get a byte from PORTC. If it is less than 100, send it to PORTB; otherwise, send it to PORTD

Bit-addressable I/O Programming

Write a C program to monitor bit RB4. If it is HIGH, send 55H toPORTC; otherwise, send AAH to PORTD

Logic Operations in C

• AND & (Ex: 0x35 & 0x0F = 0x05)

• OR | (Ex: 0x04 | 0x68 = 0x6C)

• XOR ^ (Ex: 0x54 ^ 0x78 = 0x2C)

• Invert ~ (Ex: ~0x55 = 0xAA)

• Shift right 3 times >>3 (Ex: 0x9A>>3 = 0x13)

• Shift left 5 times <<5 (Ex: 0x06 <<4 = 0x60)

Can you demonstrate using logic gates?

Data Conversion programs in C

• ASCII Numbers– Used in data transmission (i.e. serial port)

• Packed BCD to ASCII conversion• ASCII to packed BCD conversion

– Used in Real-Time Clock (RTC) module

Checksum byte in ROM

• Please refer Example 7-26 in the textbook

PIC18F4580 Pin Diagram

/AN10/AN8

/AN9

RE3/

RA7/

*Additional functions in PIC18F4580 as compared to PIC18F458

PIC18 Configuration RegistersImportant CONFIG:

•config OSC (oscillator)

•config BOR (brown-out reset)

•config BORV (brown-out reset voltage)

•config PWRT (power-up timer)

•config WDT (watchdog timer)

•config DEBUG (in-circuit debugger)

•config LVP (low voltage programming)

•config STVR (stack overflow)

*these config is also known as FUSES

CONFIG Settings

*We will be using this config settings throughout this course unless stated or otherwise

End of Chapter 1