Question

What is size of bit addressable memory in 8051 microcontroller?

• A. 16 bytes
• B. 32 bytes
• C. 64 bytes
• D. 128 bytes

Hint:

In the 8051 RAM map:
- $00\text{H}$ to $1\text{FH}$ (32 bytes) $\rightarrow$ Register Banks.
- $20\text{H}$ to $2\text{FH}$ (16 bytes) $\rightarrow$ Bit-Addressable space.
- $30\text{H}$ to $7\text{FH}$ (80 bytes) $\rightarrow$ Scratchpad RAM.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the total size (in bytes) of the bit-addressable internal RAM space within a standard 8051 microcontroller.

Step 2: Key Formula or Approach:
The internal RAM of the 8051 microcontroller consists of 128 bytes (address range $00\text{H}$ to $7\text{FH}$).
This space is segmented into register banks, bit-addressable memory, and general-purpose scratchpad RAM.

Step 3: Detailed Explanation:

• The bit-addressable RAM space occupies the byte addresses starting from $20\text{H}$ to $2\text{FH}$.

• Calculating the number of bytes in this range:
\[ 2\text{FH} - 20\text{H} + 1 = 16\text{ bytes} \]

• Since each byte contains 8 bits, the total number of individually addressable bits in this space is:
\[ 16\text{ bytes} \times 8\text{ bits/byte} = 128\text{ bits} \]

• These bits have addresses ranging from $00\text{H}$ to $7\text{FH}$.

• The question asks for the "size of memory", which is expressed in bytes, so the answer is 16 bytes.

Step 4: Final Answer:
The size of the bit addressable memory is 16 bytes, which corresponds to Option (A).