# Difference between revisions of "ADC"

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''r'' is a CPU register as specified in the table below. | ''r'' is a CPU register as specified in the table below. | ||

− | <center><table style="border: 1px | + | <center><table style="border: 1px black"><caption>OP Code Instructions:</caption> |

<tr><td>#</td><td>Register (in place of ''r'')</td></tr> | <tr><td>#</td><td>Register (in place of ''r'')</td></tr> | ||

<tr><td>8F</td><td>A</td></tr> | <tr><td>8F</td><td>A</td></tr> |

## Revision as of 21:30, 24 October 2010

## Add With Carry

This opcode group adds the contents of the specified byte-valued input and the register F *carry* flag (Flag computed as a 1 or a 0) to the contents of register A, to be stored in register A.
The formula can be seen as A=A+r+CY. Since register A is an 8-bit register, you must make sure it wraps around appropriately to only contain an 8-bit value in the range of 0-0xFF (0-255).

The ADC operation code groups are known as follows:

1) *ADC A, r*

2) *ADC A, n*

3) *ADC A, (HL)*

**Register F Flag Computation**

The *subtract* flag bit is *always* reset to 0 for any ADC operation.
The *zero* flag bit is set to 1 if the operation sets register A to 0, otherwise the *zero* flag is reset to 0.
The *carry* flag bit is set to 1 if the operation causes a mathematical carry from bit 7.
The *half-carry* flag bit is set to 1 if the operation causes a mathematical carry from bit 3.

**ADC A, r**

Machine Cycle Count: 1

*r* is a CPU register as specified in the table below.

# | Register (in place of r) |

8F | A |

88 | B |

89 | C |

8A | D |

8B | E |

8C | H |

8D | L |

**ADC A, n**

Machine Cycle Count: 2

OP Code #CE

*n* is the value of the byte of memory stored at the current immediate value, where the program counter is the 16-bit memory address being accessed.

**ADC A, (HL)**

Machine Cycle Count: 2

OP Code #8E

*(HL)* is the value of the byte of memory stored at a certain location, where the address is the 16-bit value of registers H and L, being that register H is the upper byte, and register L is the lower byte.