Sub subtract instruction, Electrical Engineering

SUB Subtract Instruction

This  instruction  is used to  subtract the contents of any  register  or memory location from  the contents of  accumulator. There are two  formats as follows:

a.Subtract the contents of Register The  contents of  register R are subtracted  from the contents of accumulator and  result of operation is  stored in the accumulator. Here register R  may be any  one  of the A, B, C,D, E,H or L registers.

SUBR                   ( A- A - R)

Flags : All  flags  are modified according to the results.

As we have already  discussed in chapter 1 that the subtraction is done  using 2 s  complement  method in microprocessor.  Followings  steps are followed  by the  8085 microprocessor while performing  subtract operations.

 Step1.  Converts subtrahend ( the  number to  be subtracted) into its 1 s complement form.

 Steps2.  Adds 1 to  the 1 complements  form to  obtain 2  complement  form the  subtrahend.

 Step3.  Adds 2 complements  to the minuend ( the  contents of the accumulator).

 Step 4.  Complements  the carry  flag.

Posted Date: 4/4/2013 7:06:46 AM | Location : United States

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