RegisterA holds the 8-bits 11011001. Determine the B operand and the logic micro-operation to be performed in order to change the value in A to: 5m Dec2005
- 01101101
- 11111101
First refer the table for Logic micro-operations which can be applied.
R1:- 1 0 1 0 (initial value) R2:- 1 1 0 0 (initial value)
| Operation name | What is the operation? | Explanation | Example |
| Selective Set | Sets those bits in Register R1 for which the corresponding R2 bit is 1. | The value 1110 suggests that selective set can be done using logic OR micro-operation.Please note that all those bits of R1, for which we have 0 bit in R2, have remained unchanged. The bits in R1 which need to be set selectively must have the corresponding R2 bits as 1. | 1010 = R11100 = R21110 |
| Selective Clear | Clear those bits in register R1 for which corresponding R2 bits are 1. | The R1 value after the operation is 0010which suggests that Corresponding micro-operation is R1 AND Compliment R2 | 1010 = R11100 = R20010 |
| Selective Complement | Complement those bits in register R1 for which the corresponding R2 bits are 1. | The R1, value 0110 after the operation suggests that the selective complement can be done using exclusive – OR micro-operation.The bits in R1 which need to be complemented selectively must have the corresponding R2 bits as 1. | 1010 = R11100 = R20110 |
| Mask Operations | Clears those bits in Register R1 for which the corresponding R2 bits are 0. | The R1 value after the operation is 1000 which suggests that the mask operation can be performed using AND micro-operation.However, the bits in R1 which are cleared or masked correspond to the bits on R2 having a 0 value. The mask operation is preferred over selective clear as most of the computers provide AND micro-operation while the micro-operation required for implementing selective clear is normally not provided in computers | 1010 = R11100 = R21000 |
| Clear | Clear all the bits | Implemented by taking exclusive OR with the same number. The exclusive OR, thus, can also be used for checking whether two numbers are equal or not. | 1010 = R11010 = R10000 |
| Insert | For inserting a new value in a bit. It is a two-step process: Step 1: Mask out the existing bit valueStep 2: Insert the bit using OR micro-operation with the bits which are to be inserted. | This is a two-step process. Example:Say contents of R1 = 0011 1011Suppose, we want to insert 0110 in place of left most 0011 then:0011 1011 (R1 before)0000 1111 (R2 for masking)
Perform AND operation (mask) 0000 1011 (R1 after) Now insert: 01100000 (R2 for insertion) Perform OR operation 0110 1011 R1 after insert
|
0011 1011 = R1we want to insert 0110 in place of left most 00110110 1011 = R1 |
Result may be different for all. You just apply the answer which comes to your mind first.
1. A 1101 1001
B 1010 0100 (Selective Complement)
—————
0110 1101
2. A 1101 1001
B 0011 1100 (Selective Set)
—————
1111 1101