PIC16F676-ESLASHP datasheet(21/130 Pages) MICROCHIP

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DS40039E-page 19

PIC16F630/676

3.0

PORTS A AND C

There are as many as twelve general purpose I/O pins

available.

Depending

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 an 6-bit wide, bi-directional port. The corre-

sponding data direction register is TRISA. Setting a

TRISA bit (= 1) will make the corresponding PORTA pin

an input (i.e., put the corresponding output driver in a

Hi-impedance mode). Clearing a TRISA bit (= 0) will

make the corresponding PORTA pin an output (i.e., put

the contents of the output latch on the selected pin).

The exception is RA3, which is input only and its TRIS

bit will always read as ‘1’. Example 3-1 shows how to

initialize PORTA.

Reading the PORTA register 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. RA3 reads ‘0’ when MCLREN = 1.

The TRISA register controls the direction of the

PORTA pins, even when they are being used as analog

inputs. The user must ensure the bits in the TRISA

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

‘0’.

EXAMPLE 3-1:

INITIALIZING PORTA

3.2

Additional Pin Functions

Every PORTA pin on the PIC16F630/676 has an

interrupt-on-change option and every PORTA pin,

except RA3, has a weak pull-up option. The next two

sections describe these functions.

3.2.1

WEAK PULL-UP

Each of the PORTA pins, except RA3, has an individu-

ally configurable weak internal pull-up. Control bits

WPUAx enable or disable each pull-up. Refer to

off when the port pin is configured as an output. The

pull-ups are disabled on a Power-on Reset by the

RAPU bit (OPTION<7>).

PORTA — PORTA REGISTER (ADDRESS: 05h)

Note:

Additional information on I/O ports may be

found in the PIC® Mid-Range Reference

Manual, (DS33023)

Note:

The ANSEL (91h) and CMCON (19h)

registers must be initialized to configure an

analog channel as a digital input. Pins

configured as analog inputs will read ‘0’.

The ANSEL register is defined for the

PIC16F676.

bcf

STATUS,RP0

;Bank 0

clrf

PORTA

;Init PORTA

movlw

05h

;Set RA<2:0> to

movwf

CMCON

;digital I/O

bsf

STATUS,RP0

;Bank 1

clrf

ANSEL

;digital I/O

movlw

0Ch

;Set RA<3:2> as inputs

movwf

TRISA

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

;as outputs

bcf

STATUS,RP0

;Bank 0

U-0

R/W-x

—

RA5

RA4

RA3

RA2

RA1

RA0

bit 7

bit 0

bit 7-6:

Unimplemented: Read as ’0’

bit 5-0:

PORTA<5:0>: PORTA I/O pin

= Port pin is >VIH

= Port pin is <VIL

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

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