PIC16LF1824 datasheet(119/440 Pages) MICROCHIP

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Preliminary

DS40001453D-page 119

PIC16(L)F1847

12.3

PORTA Registers

12.3.1

DATA REGISTER

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

corresponding data direction register is TRISA

(Register 12-4). 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). The exception is RA5, which is

input only and its TRIS bit will always read as ‘1’.

Example 12-1 shows how to initialize PORTA.

Reading the PORTA register (Register 12-3) 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 (LATA).

12.3.2

DIRECTION CONTROL

The TRISA register (Register 12-4) 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 12-1:

INITIALIZING PORTA

12.3.3

WEAK PULL-UPS

Each of the PORTA pins has an individually configurable

internal weak pull-up. Control bit WPUA<5> enables or

disables the pull-up (see Register 12-6). The weak

pull-up is automatically turned off when the port pin is

configured as an output. The pull-up is disabled on a

Power-on

Reset

the

WPUEN

bit

the

OPTION_REG register.

12.3.4

ANALOG CONTROL

The ANSELA register (Register 12-7) is used to

configure the Input mode of an I/O pin to analog.

Setting the appropriate ANSELA bit high will cause all

digital reads on the pin to be read as ‘0’ and allow

analog functions on the pin to operate correctly.

The state of the ANSELA bits has no affect on digital

output functions. A pin with TRIS clear and ANSEL set

will still operate as a digital output, but the Input mode

will be analog. This can cause unexpected behavior

when executing read-modify-write instructions on the

affected port.

The TRISA register (Register 12-4) 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’.

Note:

The ANSELA 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 LATA

;Data Latch

CLRF

LATA

;

BANKSEL ANSELA

;

CLRF

ANSELA

;digital I/O

BANKSEL TRISA

;

MOVLW

0Ch

;Set RA<3:2> as inputs

MOVWF

TRISA

;and set RA<7:4,1:0>

;as outputs

Note:

The ANSELA register must be initialized

to configure an analog channel as a digital

input. Pins configured as analog inputs

will read ‘0’.

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