The Carry Flag

The Carry flag is a bit which indicates if the result of an operation results in a value greater than 255 or less than 0. The flag will change state on both accumulator and X register operations.

Related Commands

  • BRC - The Branch if Carry Flag Set Command

  • BCC - The Branch if Carry Flag Cleared Command

  • SHR - The Shift Right Command

  • SHL - The Shift Left Command

  • ROR - The Roll Right Command

  • ROL - The Roll Left Command

The DIV and MUL commands clear the carry flag.

Examples

Example 1

{
LDA #0
CMP #5  //0-5=-5, Carry flag is set
BRC WillBranch

LDA #255
INC     //255+1=256, Carry flag is set
BRC WillBranch

LDA #200
ADD #70 //200+70=270, Carry flag is set
BRC WillBranch

LDA #0
DEC     //0-1=-1, Carry flag is set
BRC WillBranch

LDA #10
CMP #5  //10-5=5, Carry flag is cleared
BCC WillBranch

LDA #10
DEC     //10-1=9, Carry flag is cleared
BRC WillNotBranch
INC     //9+1=10, Carry flag is still cleared
BCC WillBranch

LDX #0
CMPX #5  //0-5=-5, Carry flag is set
BRC WillBranch
}

Example 2

Task1()
{
    Name="Dipswitch checker"    //Branches on the highest dipswitch set
    LDA ^59,0           //Get the dipswitch port
    ROL                 //Move Dipswitch 8 into the carry flag
    BRC DipSwitch8Set   //If carry flag is set branch.
    ROL                 //Move next Dipswitch into the carry flag
    BRC DipSwitch7Set   //If carry flag is set branch.
    ...
}