chapter 3 - input output ports programming

8/10/2019 Chapter 3 - Input Output Ports Programming

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PIC18 has many ports Depending on the family member Depending on the number of pins on the chip

Each port can be configured as input or output. Bidirectional port

Each port has some other functions Such as timer , ADC, interrupts and serial communication.

Some ports have 8 bits, while others have not


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PIC18F4550 connection diagram


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Features and Functions

In order pins operation can match internal 8-bitorganization, (all of them are similar to registers)grouped into five so called ports denoted by A, B, C, Dand E. They all have several features in common: many I/O pins have two or three functions. If a pin is

used as any other function, it may not be used as ageneral purpose input/output pin

Every port has its corresponding TRIS register:TRISA, TRISB, TRISC etc. which determinesperformance, but not the contents of the port bits.


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By clearing some bit of the TRIS register(bit=0), the corresponding port pin isconfigured as output .

By setting some bit of the TRIS register(bit=1), the corresponding port pin isconfigured as input .

This rule is easy to remember 0 = Output, 1 = Input


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PIC pin functionsetting


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Example: Port A as Output


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Example: Port A as Input


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Example: more efficient way to set port asinput or output


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Read followed by writeoperation

Be careful Dont have two I/O operations one right after

the others.

Data Dependency A NOP is needed to make that data is written

in the WREG before it read for outputting to

PortB


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Dual role of microcontroller port

Port A and B Port A usually multiplexed with Analog to Digital converter to

save I/O pins. Port A seldom used for simple I/O operation

Port A Port B


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Port C and D (alternate function)



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Port E (alternate function) Port E occupies a total of 3 pin (RE0-RE2) for

3 additional analog input or I/O.

AN5, AN6 and AN7


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I/O Bit Manipulation Programming

I/O ports and bit-addressability

Monitoring a single bit Reading a single bit


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I/O ports and bit addressabilitySingle bit addressability for PIC18


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Bit Oriented Instruction for PIC18

Single bit (Bit oriented) instruction for PIC18


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BSF (bit set fileReg)

Used to set HIGH for a single bit in fileReg The Syntax :

BSF fileReg, bit_num


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BCF(bit clear fileReg)

Used to clear a sigle bit of given fileReg The Syntax:

BCF fileReg, bit_number


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Checking an input pin

To make decisions base on the status of agiven bit in the file register, we use: BTFSC (bit test fileReg skip if clear) BTFSS (bit test fileReg skip if set)

These single-bit instruction allow tomonitor a single bit and make decisionwhether it is 0 or 1.


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Reading a single bit

We can use bit test instruction to read thestatus of the single bit and send it toanother bit of save it


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Reading input pins VS. LATxport


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chapter 3 - input output ports programming

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