8051 bit set instruction and bit addresses Consider the 8051 statement: SETB 01H Does this instruction set the bit at bit address 01H to logic 1?

Introduction / Context:
The 8051 includes instructions for single bit manipulation. SETB sets a specified bit to logic 1. Bits may refer to SFR bits or bits in the bit-addressable low RAM region. Understanding how numeric bit addresses map to byte addresses is key to using these instructions correctly.

Given Data / Assumptions:

• Instruction is SETB 01H with a numeric bit address.
• Bit addresses 00H to 7FH correspond to low RAM bit space mapped onto bytes 20H to 2FH.
• No operand refers to R0 or R1, so this is not indirect addressing.

Concept / Approach:

SETB bit_address sets the specified bit to 1. The low RAM bit space uses a linear mapping: bit_address = (byte_address * 8) + bit_index. The lowest bit address 00H corresponds to byte 20H bit 0; therefore 01H corresponds to byte 20H bit 1. The instruction is valid and performs a set operation.

Step-by-Step Solution:

Verification / Alternative check:

Assemble and single step in a simulator: memory byte 20H toggles bit 1 to 1; PSW flags are unaffected.

Why Other Options Are Wrong:

False: contradicts the defined behavior of SETB.

It clears the bit: would be the effect of CLR, not SETB.

Invalid address: 01H is valid within the 00H–7FH bit address range.

Common Pitfalls:

Confusing bit addresses with byte addresses and assuming all bytes are bit-addressable. Only the 20H–2FH byte range and specific SFRs support bit addressing.

Final Answer:

True