8051 internal RAM bit-addressable area Identify the byte address range that is bit-addressable in the internal data memory.

Introduction / Context:
The 8051 architecture supports direct bit manipulation for selected areas of memory. Bit-addressability enables instructions such as SETB, CLR, JB, and JNB to operate on single bits efficiently. Correctly identifying the bit-addressable byte range is essential for mapping application flags and control bits into the low internal RAM area.

Given Data / Assumptions:

• The question pertains to the internal data RAM of a standard 8051.
• Byte addresses are in hexadecimal.
• Bit-addressable bytes correspond to specific bit addresses from 00H to 7FH.

Concept / Approach:

In a classic 8051, the 16 bytes from 20H to 2FH form a 128-bit region that is bit-addressable. Each byte contains 8 individually addressable bits, making 16 * 8 = 128 bit locations. Bit addresses 00H to 7FH map directly onto this region.

Step-by-Step Solution:

Verification / Alternative check:

Device memory maps and assembler include files confirm that only 20H–2FH in low RAM and selected SFR bits are bit-addressable. Attempts to set a bit at bytes outside this range with direct bit addresses will assemble to SFR bit operations, not low RAM bits.

Why Other Options Are Wrong:

10H–1FH and 30H–3FH and 40H–4FH are normal byte-addressable areas in low RAM and are not low RAM bit-addressable blocks.

Common Pitfalls:

Confusing bit-addressable low RAM with bit-addressable SFR bits, and assuming the entire low RAM supports single-bit operations.

Final Answer:

20H through 2FH