1. Bit Manipulation in 'C' 'C' bit operators
OP symbol Description Example
& AND y = y & 0xF7;
| OR y = y | 0x08;
^ XOR
>> n shift bits right n places y = y >> 4;
<< n shift bits left n places y = y << 2;
~ complements (invert all bits) y = ~y;
Only use with integer data types - Not real types.
Note: In 'C' binary operators(such as y = y OP z;) can be written as in a shortened form: y OP= z;
E.g.'s y = y + 7; y+=7;
y = y & 0x80; y &= 0x80;
y = y >> 4; y >>= 4;

2. Masking for bit manipulation
Masking uses AND and OR operators
Use OR ('|') to set bits to '1'
Use AND ('&') to set bits to 0
Use XOR(^) to toggle bits (0 -> 1 and 1-> 0) OR A B
Output 1
AND A B
Output 1
XOR A B
Output 1

3. Output Masking Setting bits to 1 using the OR (|) bit-wise operator
General format: value = value | mask;
Shorthand : value |= mask;
Mask bits : '1' to set a bit, '0' to leave bit unchanged.
Setting bits to 0 using the AND (&) bit-wise operator
General format: value = value & mask;
Shorthand : value &= mask;
Mask bits : '0' to clear a bit, '1' to leave bit unchanged
Example: Controlling a single bit (Note VAR is an 8-bit integer data type.)
To set bit 3 to '1' the mask is
VAR= VAR | 0x08;
To set bit 3 to '0' the mask is
VAR = VAR & 0xf7;

4. More examples
For 32 bit integer data types: FIO2PIN |= 0x ; // ? FIO2PIN &= 0xFFFBFFFF; FIO2PIN |= ~0x ;
Changing several bits in one operation
FIO2PIN |= 0x00FF0000;
FIO2PIN |= 0x ;
PIO2PIN &= ~ 0x ;
Toggling bits using XOR (^)
FIO2PIN ^= 0x
FIO2PIN |= 0x ; // set bit 18 FIO2PIN &= 0xFFFBFFFF; // clear bit 18 FIO2PIN |= ~0x ; // clear bit 18
Changing multiple bits
FIO2PIN |= 0x00FF0000; // set bits 16 thro' 23
FIO2PIN |= 0x ; //set bits 4 and 12
PIO2PIN &= ~ 0x ; //clear bits 4 and 12
Toggling bits using XOR (^)
FIO2PIN ^= 0x ; //toggle bit 7

5. Input Masking When a single bit need to be tested
Use AND (&) and a mask to isolate the selected bit
value & mask
Used in input Polling to test an individual input bit
Example: Testing bit 3
if mask is (0x08)
Two possible results or when ANDED
I.e. zero or non-zero
Loop while bit is '0', exit when bit becomes 1
while( (VAR & 0x08) == 0) { ; }
Loop while bit is '1', exit when bit becomes 0
while( (VAR & 0x08) != 0) { ; }

6. More examples
if ((FIO2PIN & 0x ) == 0) { FIO2PIN |= 0x ; } if (FIO2PIN & 0x ) != 0) FIO2PIN &= ~0x ; if(FIO2PIN & 0x000000F0) == 0x000000F0) FIO2PIN ^= 0x ;
If bit 7 is 0 then set bit 0
if bit 2 is 1 then clear bit 3
if bits 4 thro' 7 are ones then toggle bit 1

7. Shift Operations << shift left >> shift right
used to move bits to the left - lose MSB and gain new LSB (new LSB = 0 for all data types)
multiplies by 2 for each shift.
>> shift right
used to move bits to the right - lose LSB and gain new MSB (new MSB = 0 for unsigned integer data types, or previous MSB for signed types).
divides by 2 for each shift.

8. Shift operations
FIO2PIN |= (1<<7); // set bit : start : : : : : : : 7 FIO2PIN &= ~(1<<23); // clear bit 23

9. Exercise
A32 bit register is interfaced to the following:- A motor connected to bit 7 (0 is off, 1 is on) An led connected to bit 0 (0 is off, 1 is on) Two switches S1 and S2 connected to bits 1 and 2 respectively that generate either logic 0 or 1 inputs.
Write C code to perform the following steps:
Loop until switch S1 is logic 1
Now turn on the led
then wait until both switches are at logic 1
Now turn on the motor
Loop until either of th eswitches is change to logic 0
Turn of the motor and the led