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Module 4: Memory and I/O Interfacing

20257m

Explain memory interfacing techniques in the 8051 microcontroller.

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Memory Interfacing Techniques in 8051

  • Linear/Low-cost: Direct high line to CS (e.g., P2.7 to ROM CS) → simple but wastes space, partial decoding.
  • Full Decoding: 74LS138 decoder from A15-A13 to select multiple devices, non-overlapping ranges (e.g., Y0 0000-1FFFH for 8K ROM, Y1 2000-3FFFH for RAM).
  • Bus Multiplexing: P0 AD0-7 via 74LS373 latched by ALE, P2 provides high address; \overline{PSEN}→ROM OE, \overline{RD}/\overline{WR}→RAM OE/WE.
  • Program vs Data: ROM to \overline{PSEN} space, RAM to MOVX space; can share same physical chip with separate controls.
  • **Example 16K ROM (27128) +8K RAM (6264) decoding as Q11: ROM 0000-3FFFH, RAM 4000-5FFFH.

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