Question

How many bytes of bit addressable memory is present in 8051 microcontroller?

• A. 32 bytes
• B. 8 bytes
• C. 16 bytes
• D. 128 bytes

Hint:

8051 bit-addressable area = 128 bits (commonly remembered).

Answer 1

The Correct Option is A

Step 1: Locate the bit-addressable RAM area.
Inside the 8051's internal RAM, the block from address 20H to 2FH is specially designed so that every single bit inside it can be accessed individually rather than a whole byte at a time. This block is 16 bytes long, which works out to $16 \times 8 = 128$ individually addressable bits.
Step 2: Remember that RAM is not the only bit-addressable area.
Bit addressing in the 8051 is not limited to that RAM block. A number of the special function registers, such as the port latches, the accumulator, PSW, and the interrupt and control registers, are also bit-addressable, since their byte addresses end in 0 or 8.
Step 3: Add the two contributions together.
These bit-addressable SFRs together contribute another 128 bits worth of addressable space, equivalent to 16 more bytes. Combining the 16 bytes from RAM with the 16 bytes worth from the bit-addressable SFR area gives a total of 32 bytes of bit-addressable memory.
\[ \boxed{32\text{ bytes}} \]