Embedded C Programming

Question 1

UnSet a specific bit in a byte (set to 0)

Answer 1

targetByte &= ~(1 &laquo_space;n); //Shifts a 1 n bits left then inverts then AND’s the values and sets the source byte to the result.

Question 2

Toggle a specifc bit in a byte (1=0 | 0=1)

Answer 2

targetByte ^= 1 &laquo_space;n; //Exclusive OR the bit shifted 1 with the source byte.

Question 3

Bitwise “OR” Operator and its’ use.

Answer 3

Or Operator is the pipe : “ | “
It is used to set individual bits, for example
REG = (1«19) | (1«12); // 19th and 12th bits are set to ‘1’ , rest are Zeros.

Question 4

Set 3rd bit of byte to 1 using bit shift…

Answer 4

(1«3)

Question 5

Operator for inverting bits

Answer 5

”~”

Bit-wise Negation Operator

Question 6

Set 11th and 4th bit of a register to 1…

Answer 6

REG |= (1 &laquo_space;11) | (1 &laquo_space;4);

Question 7

Syntax and format of ternary operator…

Answer 7

result = binaryCondition ? valueReturnedIfTrue : valueReturnedIfFalse;

Question 8

”~”

Answer 8

Bit-wise Negation Operator, used for the inversion of bits.

Question 9

Check value of individual bit in byte

Answer 9

(targetByte&raquo_space; n) & 1; //Compares shifted value to see if AND’d byt with 0x01 returns a 1

Question 10

Set a specific bit in a byte

Answer 10

targetByte |= (1<

Question 11

How do you set a subset of bits in a value?

Answer 11

Bitwide OR'ing
uint8_t mask = 0x0F;    //00001111b
uint8_t value = 0x55;    //01010101b
output = mask | value; value;
output = 0x05;  //00000101b

Question 12

Proper use scenarios for the “voltaile” keyword

Answer 12

A variable should be declared volatile whenever its value could change unexpectedly. In practice, only three types of variables could change:

1. Memory-mapped peripheral registers
2. Global variables modified by an interrupt service routine
3. Global variables accessed by multiple tasks within a multi-threaded application

Question 13

How do you extract a certain subset of bits from a value?

Answer 13

Bitwide ANDing
uint8_t mask = 0x0F;    //00001111b
uint8_t value = 0x55;    //01010101b
output = mask & value;
output = 0x05;  //00000101b

common uses : extracting individual bytes from a word (would utilize shifting as well)

Question 14

Binary “AND” operator and it’s uses

Answer 14

“&” Binary AND Operator
Used to check condition of individual bits, usually performed using bit masking. For example:
reg1 = 0x2A
a = reg1 & (1 &laquo_space;3); //0x2A & 0x

Question 15

”|=” uses

Answer 15

Used to set individual bits of a byte without interfering with the status of other bits. This is done by masking