Lecture 4-IO Port Programming

8/13/2019 Lecture 4-IO Port Programming

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Microprocessor System

Lecture 4 : IO Port Programming


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PIN Diagram


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Pins XTAL1 and XTAL2


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Pin RST


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D Flip-Flop

Edge-Trigger

Each pin of port 0, port 1, port 2, and

port 3 has a D Flip-Flop.


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Push-Pull Output


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Open Source


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Open Drain


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Port 0 (1)

Each pin of port 0 must be connectedexternally to a 10K ohm pull-up register.


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Port 0 (3)

Example:

MOV A, #55H

Back: MOV P0, A

ACALL DELAY

CPL A

SJMP BACK


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Port 0 (4)

Example:

MOV A, #0FFH

MOV P0, A

Back: MOV A, P0

MOV P1, A

SJMP BACK


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Port 1 It can be used for input or output.

Port 1 is configured as an output port uponreset.

Port 1.x is configured as an input bit by

writing 1 to bit x of port 1. Port 1 isconfigured as an input port by writing 1 to

all the bits.


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Port 3 It can be used for input or output.

Port 3 is configured as an output port upon reset.Port 3.x is configured as an input bit by

writing 1 to bit x of port 3. Port 3 is

configured as an input port by writing 1 to

all the bits. It provides alternate

functions.


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Pins EA, PSEN, and ALE

EA (external access): EA is connected to VCC if code is stored in on-

chip ROM such as 8051 family.

EA is connected to Ground if code is stored inexternal ROM such as 8031.

PSEN (program store enable): PSEN is connected to OE of external ROM.

ALE (address latch enable):ALE is used to de-multiplexing the address and

data.


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Single-Bit Address of Ports

Lecture 4-IO Port Programming

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