Question

1. Write code to turn on bit 4 of PORTC, where bit 4 is configured as output bit.

2. What does this code in assembly do? You can write your answer in a high-level language like C.

MOVF Q,W

SUBWF P,F

Answer 1

Ans.

1)

C code:

#include<p18f452.h>
int main()
{
TRISC.F3 = 0; //Configure 4th bit of PORTC as Output.
PORTC.F3 = 1; //Turn on 4th bit of PORTC.
return (0);
}

2)

MOVF Q,W :

It is used to move contents of Q register , if W=0,contents of Q register is moved to Working register WREG. If W=1,the contents of register Q is copied to itself this is used to check if a register has value zero as when the value is copied to itself the zero flag is affected ie, if the content is zero after this instructon z flag goes high.

SUBWF P,F :

Substracts W register from P register and if F is 0 result is stored in WREG (Working register) else if F is 1, result is stored back to the file register P.