8051 internal memory map understanding Are special function registers (SFRs) located in the next 128 addresses immediately above the lower 128 bytes of internal RAM?
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ATrue
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BFalse
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COnly on the 8052, not on the 8051
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DOnly when EA is HIGH
Answer
Correct Answer: True
Explanation
Introduction / Context:The 8051 has a distinctive internal address map: lower internal RAM and upper special function registers share the same 8-bit address space but map to different functional regions. This question probes recognition of the address ranges involved.
Given Data / Assumptions:
- Lower internal RAM occupies addresses 0x00–0x7F (128 bytes).
- Special function registers are mapped at 0x80–0xFF.
- Direct addressing to 0x80–0xFF targets SFRs, not general RAM.
Concept / Approach:Conceptually, SFRs reside in the “next 128 locations” above the lower RAM block in the direct address space: 0x80–0xFF. These are not general-purpose RAM bytes; they control peripherals, ports, timers, serial, and CPU status. Indirect addressing cannot access SFRs; it wraps within lower RAM (and upper RAM on 8052), reinforcing the separation.
Step-by-Step Solution:
1) Identify lower RAM: 128 bytes at 0x00–0x7F.2) Identify SFR region: 128 byte-wide address map at 0x80–0xFF.3) Direct addressing to 0x80–0xFF accesses SFRs (for example, P0 = 0x80, TMOD = 0x89).4) Conclude that SFRs lie in the next 128 addresses above lower RAM in direct address terms.Verification / Alternative check:Check any 8051 memory map: SFRs occupy addresses 0x80–0xFF.
Why Other Options Are Wrong:
- False: Disagrees with the standard 8051 map.
- Only on 8052: 8052 adds upper 128 RAM via indirect addressing, but SFR map remains 0x80–0xFF on both.
- Only when EA is HIGH: EA relates to code memory selection, not SFR mapping.
Common Pitfalls:Assuming SFRs are normal RAM, or trying to access SFRs with indirect addressing.
Final Answer:True