Question

On power up, the 8051 uses which RAM locations for register R0–R7?

• A. 00–07
• B. 00–2F
• C. 00–7F
• D. 00–FF

Hint:

Default register bank = Bank 0 → addresses 00H–07H.

Answer 1

The Correct Option is A

Step 1: Recall what happens at power-up.
When the 8051 is powered on or reset, all its control bits start at their default state, which includes the bank-select bits RS1 and RS0 both being cleared to 0.
Step 2: Identify which bank that selects.
With $RS1RS0 = 00$, register bank 0 is the one that becomes active by default, and it is this bank that the mnemonics R0 through R7 refer to right after reset.
Step 3: Map bank 0 onto actual RAM addresses.
Each of the four register banks occupies exactly 8 consecutive bytes of internal RAM, and bank 0 is placed right at the very bottom of memory, so R0 sits at address 00H and R7 sits at address 07H.
\[ \boxed{00\text{H to }07\text{H}} \]