8051 external data memory interface (MOVX space) What is the maximum external data memory capacity that can be interfaced to the 8051?
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A32K
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B64K
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C128K
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D256K
Answer
Correct Answer: 64K
Explanation
Introduction / Context:The 8051 can address on-chip RAM plus external data memory through the MOVX instruction. Understanding the external memory address space is important for system design and memory mapping.
Given Data / Assumptions:
- Classic 8051 external data memory bus with 16-bit addressing.
- Separate program and data spaces (Harvard-like architecture).
- Focus is on external data memory capacity.
Concept / Approach:With a 16-bit address for external data memory, the addressable range is 2^16 bytes = 65,536 bytes = 64 KB. This is accessed via MOVX using DPTR or Ri (for paged modes on some variants).
Step-by-Step Solution:
1) External data space uses 16 address lines.2) Capacity = 2^16 bytes = 65,536 bytes.3) 65,536 bytes ≈ 64 KB.4) Therefore, the correct capacity is 64K.Verification / Alternative check:Memory interfacing examples in 8051 textbooks consistently show 64 KB external data space with latches to demultiplex address/data lines (ALE).
Why Other Options Are Wrong:
- 32K: half the actual address space.
- 128K or 256K: exceed the 16-bit addressing limit of the standard external data space.
Common Pitfalls:Confusing external data memory size with external program memory size; both are 64 KB separately, but they are distinct spaces in the classical architecture.
Final Answer:64K