2 Basics of C

Question 1

The structure that both ASM and C share?

Answer 1

• Configuration bits
• Variable storage
• Entry Point
• Ininite loop

Question 2

STRUC: What are the configuration bits?

Answer 2

These configure the basic setup of the PIC including things like the oscillator type and the presence of the watch dog timer

Question 3

STRUC: What is variable storage setup?

Answer 3

Definitions of variables, including where in memory to store them

Question 4

STRUC: Entry point

Answer 4

An indicator of where in the code the program counter will start

Question 5

STRUC: Infinite loop?

Answer 5

An infinite loop is commonly used to keep repeating a set of operations ad infinitum

Question 6

Config(Role/Default): FOSC?

Answer 6

The type of oscillator to use (external/internal/crystal)

Default: XT(external crystal)

Question 7

Config(Role/Defult): WDTE?

Answer 7

Enable/Disable the watch dog timer

OFF(no wdt)

Question 8

Config(Role/Defult): PWRITE?

Answer 8

Enable/Disable the power-up timer (72 ms)

ON(power-up timer)

Question 9

Config(Role/Defult): CP?

Answer 9

Enable/Disable code protection

OFF(code protection)

Question 10

Configuration bits for LED flash?

Answer 10

pragma config FOSC = XT // XT oscillator

// Setup configuration bits

Question 11

Configure oscillator frequency for flashing LED?

Answer 11

define _XTAL_FREQ 4000000

// Oscillator Frequency (4 MHz)

Question 12

Flashing LED: Code to import library functions?

Answer 12

include

// Include C library functions for PIC

Question 13

Flashing LED: Code to write to ports?

Answer 13

PORTBbits.RB0 = 1; // Set RB0 high __delay_ms(500); // Wait 0.5 seconds PORTBbits.RB0 = 0; // Set RB0 low __delay_ms(500); // Wait 0.5 seconds

Question 14

Flashing LED: Port Setup?

Answer 14

// Set all port B bits to be output

TRISB = 0x0;

Question 15

Flashing LED: Main loop for the program?

Answer 15

Question 16

A statement?

Answer 16

A statement is the smallest standalone element of a program, normally a single line of code

Question 17

In C a statement must be terminated with a ….

Answer 17

semicolon

Question 18

C: Blocks?

Answer 18

Statements can be grouped together into blocks, for example blocks of code that form part of a loop

Question 19

C: Example of a block?

Answer 19

Question 20

Advantages of C in terms of I/O?

Answer 20

We can read or write to individual pins as well as to the entire PORT register (this is a bit more powerful than ASM)

Question 21

Example in C of writing to a port?

Answer 21

Question 22

C program to Toggle an LED based on a user keypress

Answer 22

Question 23

Differences between ASM and C in variable naming?

Answer 23

• In assembler we had to specify exactly where in memory a variable would live, this was tedious and does not port well to other PICs
• In C life is much better, and all we need to do is give our variables a name and a type, for our small PIC we will only use integers

Question 24

Creating variables in C?

Answer 24

Question 25

C: Restrictions on variable names?

Answer 25

• Just like in assembler, you must declare variables before you use them e.g int age;
• Otherwise, the compiler doesn’t know what they are!
• Variable names can contain letters (a-z, A-Z), digits (0-9) and underscores ( _ )
• They must start with a letter or an underscore (but not a digit)
• C keywords are not allowed e.g. if for do int . . .