PIC12F635ESS datasheet(49/234 Pages) MICROCHIP

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DS41232D-page 47

PIC12F635/PIC16F636/639

4.0

I/O PORTS

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.

4.1

PORTA and the TRISA Registers

PORTA is a 6-bit wide, bidirectional port. The

corresponding

data

direction

TRISA

(Register 4-2). Setting a TRISA bit (= 1) will make the

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

corresponding output driver in a High-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 4-1 shows how to initialize

PORTA.

Reading the PORTA register (Register 4-1) 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. RA3 reads ‘0’ when MCLRE = 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 inputs always

read ‘0’.

EXAMPLE 4-1:

INITIALIZING PORTA

4.2

Additional Pin Functions

Every PORTA pin on the PIC12F635/PIC16F636/639

has an interrupt-on-change option and a weak

pull-up/pull-down option. RA0 has an Ultra Low-Power

Wake-up option. The next three sections describe

these functions.

4.2.1

WEAK PULL-UP/PULL-DOWN

Each of the PORTA pins, except RA3, has an internal

weak pull-up and pull-down. The WDA bits select either

a pull-up or pull-down for an individual port bit.

Individual control bits can turn on the pull-up or

pull-down. These pull-ups/pull-downs are automatically

turned off when the port pin is configured as an output,

as an alternate function or on a Power-on Reset,

setting the RAPU bit of the OPTION register. A weak

pull-up on RA3 is enabled when configured as MCLR

in the Configuration Word register and disabled when

high

voltage

detected,

reduce

current

consumption through RA3, while in Programming

mode.

Note:

PORTA = GPIO

TRISA = TRISIO

Note:

The CMCON0 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

MOVLW

07h

;Set RA<2:0> to

MOVWF

CMCON0

;digital I/O

BSF

STATUS,RP0

;Bank 1

BCF

STATUS,RP1

;

MOVLW

0Ch

;Set RA<3:2> as inputs

MOVWF

TRISA

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

;as outputs

Note:

PORTA = GPIO

TRISA = TRISIO

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