The mask logical micro-operation is equivalent to which logical gate?
AND gate
Understanding the Mask Logical Micro-operation
The question asks us to identify the logical gate that is equivalent to the mask logical micro-operation. In computer architecture and digital logic, logical micro-operations perform bitwise operations on data stored in registers. Masking is a common technique that uses one word (the mask) to modify another word by selectively clearing, setting, or complementing bits.
What is Masking?
Masking typically involves using a logical operation between the data word and a mask word. One common application of masking is to clear specific bits in a data word while leaving others unchanged. For example, if you want to keep certain bits and set others to zero, you would use a mask.
The Role of Logical Gates
Logical micro-operations are implemented using combinational circuits built from basic logic gates. We need to figure out which basic logical gate performs the bitwise operation characteristic of clearing bits with a mask.
Analyzing the Options and the Correct Gate (AND Gate)
Let's examine the behavior of the AND gate in a bitwise context. The AND gate outputs 1 only if both inputs are 1. If one input is 0, the output is 0. Consider a data bit (D) and a corresponding mask bit (M). The operation performed is DataBit AND MaskBit.
| Data Bit (D) | Mask Bit (M) | D AND M (Output) |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
Observe the results:
- If the mask bit (M) is 0, the output (D AND M) is always 0, regardless of the data bit (D). This effectively clears the data bit.
- If the mask bit (M) is 1, the output (D AND M) is equal to the data bit (D). This leaves the data bit unchanged.
This behavior perfectly matches the common requirement of a mask operation used to clear specific bits: bits corresponding to 0s in the mask are cleared, and bits corresponding to 1s in the mask are preserved.
For example, to clear the lower 4 bits of an 8-bit register containing the value \( 11010110_2 \), you would use a mask \( 11110000_2 \). The operation would be:
\( 11010110_2 \)
AND \( 11110000_2 \)
---------
\( 11010000_2 \)
The higher 4 bits are preserved (because the mask bits are 1), and the lower 4 bits are cleared to 0 (because the mask bits are 0).
Why Other Gates are Not Equivalent for Masking (Clearing)
- OR gate: The OR operation sets a bit if the mask bit is 1. \( \text{DataBit OR 1} = 1 \), \( \text{DataBit OR 0} = \text{DataBit} \). This is used for setting bits, not clearing.
- NOR gate: The NOR gate is the inverse of OR. \( \text{DataBit NOR MaskBit} = \overline{\text{DataBit OR MaskBit}} \). It doesn't perform the selective clear/preserve function of masking.
- NAND gate: The NAND gate is the inverse of AND. \( \text{DataBit NAND MaskBit} = \overline{\text{DataBit AND MaskBit}} \). It doesn't perform the selective clear/preserve function of masking.
Therefore, the AND gate's behavior is equivalent to the mask logical micro-operation used for clearing bits.
Revision Table: Logical Gate Behavior
| Operation | Mask Bit = 0 | Mask Bit = 1 | Primary Use Case in Masking Context |
|---|---|---|---|
| Data AND Mask | Result = 0 (Clears Data Bit) | Result = Data Bit (Preserves Data Bit) | Clearing specific bits |
| Data OR Mask | Result = Data Bit (Preserves Data Bit) | Result = 1 (Sets Data Bit) | Setting specific bits |
| Data XOR Mask | Result = Data Bit (Preserves Data Bit) | Result = \(\overline{\text{Data Bit}}\) (Complements Data Bit) | Toggling specific bits |
Additional Information: Bitwise Operations
Bitwise logical micro-operations are fundamental in computer programming and digital hardware. They operate on individual bits of data words independently. Common bitwise operations include AND, OR, XOR, and NOT. Masking is a technique that leverages these bitwise operations to manipulate data at the bit level. The choice of AND, OR, or XOR for masking depends on whether you want to clear, set, or toggle bits, respectively. The question specifically refers to "the mask logical micro-operation," which most commonly implies the use of AND for clearing bits or isolating a portion of a word.
Important Questions from Number Representations and Computer Arithmetic
Which is the largest unit of storage among the following?
The operations executed on data stored in registers are known as-
What is the binary representation of 35?
- A register contains a 3's complement number 10100. If it is divided by 2, find the value of the register.
- The IEEE-754 double-precision format to represent floating point numbers, has a length of _____ bits.
