PIC16F636T-I/SL(2005) View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

PIC16F636T-I/SL
(Rev.:2005)

8/14-Pin Flash-Based, 8-Bit CMOS Microcontrollers with nanoWatt Technology

Microchip Technology 

PIC12F635/PIC16F636/639

4.0 I/O PORTS

There are as many as twelve 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.

4.1 PORTA and the TRISA Registers

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

corresponding data direction register is TRISA

(Register 4-4). 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 4-3) 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

register are maintained set when using them as analog

inputs. I/O pins configured as analog inputs always

read ‘0’.

Note:

The CMCON0 (19h) register must be

initialized to configure an analog channel

as a digital input. Pins configured as

analog inputs will read ‘0’.

EXAMPLE 4-1: INITIALIZING PORTA

BCF

BCF

CLRF

MOVLW

MOVWF

BSF

BCF

MOVLW

MOVWF

STATUS,RP0

STATUS,RP1

PORTA

07h

CMCON0

STATUS,RP0

STATUS,RP1

0Ch

TRISA

BCF STATUS,RP0

BCF STATUS,RP1

;Bank 0

;

;Init PORTA

;Set RA<2:0> to

;digital I/O

;Bank 1

;

;Set RA<3:2> as inputs

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

;as outputs

;Bank 0

;

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 (OPTION_REG<7>). A weak pull-

up on RA3 is enabled when configured as MCLR in the

Configuration Word register and disabled when high

voltage is detected, to reduce current consumption

through RA3, while in Programming mode.

Note: PORTA = GPIO

TRISA = TRISIO

© 2005 Microchip Technology Inc.

Preliminary

DS41232B-page 39

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