PIC16F882-I datasheet(41/328 Pages) MICROCHIP

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DS41291F-page 39

PIC16F882/883/884/886/887

3.0

I/O PORTS

There are as many as thirty-five general purpose I/O

pins available. Depending on which peripherals are

enabled, some or all of the pins may not be available as

general purpose I/O. In general, when a peripheral is

enabled, the associated pin may not be used as a

general purpose I/O pin.

3.1

PORTA and the TRISA Registers

PORTA is a 8-bit wide, bidirectional port. The

corresponding

data

direction

TRISA

(Register 3-2). Setting a TRISA bit (= 1) will make the

corresponding PORTA pin an input (i.e., disable the

output driver). Clearing a TRISA bit (= 0) will make the

corresponding PORTA pin an output (i.e., enables

output driver and puts the contents of the output latch

on the selected pin). Example 3-1 shows how to

initialize PORTA.

Reading the PORTA register (Register 3-1) reads the

status of the pins, whereas writing to it will write to the

PORT latch. All write operations are read-modify-write

operations. Therefore, a write to a port implies that the

port pins are read, this value is modified and then

written to the PORT data latch.

The TRISA register (Register 3-2) controls the PORTA

pin output drivers, even when they are being used as

analog inputs. The user should ensure the bits in the

TRISA register are maintained set when using them as

analog inputs. I/O pins configured as analog input always

read ‘0’.

EXAMPLE 3-1:

INITIALIZING PORTA

Note:

The ANSEL register must be initialized to

configure an analog channel as a digital

input. Pins configured as analog inputs will

read ‘0’.

BANKSEL PORTA

;

CLRF

PORTA

;Init PORTA

BANKSEL ANSEL

;

CLRF

ANSEL

;digital I/O

BANKSEL TRISA

;

MOVLW

0Ch

;Set RA<3:2> as inputs

MOVWF

TRISA

;and set RA<5:4,1:0>

;as outputs

PORTA: PORTA REGISTER

R/W-x

RA7

RA6

RA5

RA4

RA3

RA2

RA1

RA0

bit 7

bit 0

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

-n = Value at POR

‘1’ = Bit is set

‘0’ = Bit is cleared

x = Bit is unknown

bit 7-0

RA<7:0>: PORTA I/O Pin bit

= Port pin is > VIH

= Port pin is < VIL

TRISA: PORTA TRI-STATE REGISTER

R/W-1(1)

R/W-1

TRISA7

TRISA6

TRISA5

TRISA4

TRISA3

TRISA2

TRISA1

TRISA0

bit 7

bit 0

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

-n = Value at POR

‘1’ = Bit is set

‘0’ = Bit is cleared

x = Bit is unknown

bit 7-0

TRISA<7:0>: PORTA Tri-State Control bit

= PORTA pin configured as an input (tri-stated)

= PORTA pin configured as an output

Note

TRISA<7:6> always reads ‘1’ in XT, HS and LP Oscillator modes.

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