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Module 2: The 8051 Architecture

20206m

Explain the alternate functions of port 0, port 2 and port 3.

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Alternate Functions of Port 0, Port 2, Port 3

  • Port 0 (AD0-AD7): Normal quasi-I/O with pull-ups, but when external memory accessed, becomes multiplexed low address/data bus latched by ALE. Open-drain, needs external pull-up for input.
  • Port 2 (A8-A15): Quasi I/O; alternately high address byte for external memory (stable during data phase). Does not need latch.
  • Port 3 (8 alternates as Q1): P3.0 RxD, P3.1 TxD, P3.2 INT0, P3.3 INT1, P3.4 T0, P3.5 T1, P3.6 WR\ (data write strobe), P3.7 RD\ (data read). Selected when corresponding SFR bit enables function; else acts as I/O.

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