DAA (BCD addition) instruction. HC12/S12

Discussion in 'Homework Help' started by Jess_88, Oct 30, 2011.

  1. Jess_88

    Thread Starter Member

    Apr 29, 2011
    Hey guys :)

    I'm having a little trouble understanding what is going on with this instruction for the question.

    The HC12/S12 has a DAA instruction which takes the result of an addition operation and corrects the result to represent the result of a Binary Coded Decimal (BCD) addition. The instruction operations are as de- scribed in the table below.

    The two numbers added together are $99 in the A register and $22 in the B register which actually represent 99 and 22 in BCD.

    a)What is the result of executing an ABA instruction and the subsequent execution of a DAA instruction in- clude the effect on the carry (C) bit of the condition code register.

    After execution of ABA Register A ___$BB___ Carry bit _______0_______
    After execution of DAA Register A ___$21___ Carry bit _______1_______

    I understand the addition of the to numbers in bcd (99 + 22 = BB), but what the heck is going on with DAA???:confused:

    can anyone explain the steps taken? (showing what bits are contributing to the DCC instruction and how they change/why?)

    thanks a bunch guys
  2. Jess_88

    Thread Starter Member

    Apr 29, 2011
    correction... I guess I don't know how to add in bcd ether :(