PIC16F1946 datasheet(127/448 Pages) MICROCHIP

127 / 448 page

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Preliminary

DS41414C-page 127

PIC16(L)F1946/1947

12.2

PORTA Registers

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

corresponding data direction register is TRISA

(Register 12-3). 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 12-1 shows how to

initialize PORTA.

Reading the PORTA register (Register 12-2) 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).

The TRISA register (Register 12-3) 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’.

12.2.1

ANSELA REGISTER

The ANSELA register (Register 12-5) 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.

EXAMPLE 12-1:

INITIALIZING PORTA

12.2.2

PORTA FUNCTIONS AND OUTPUT

PRIORITIES

Each PORTA pin is multiplexed with other functions. The

pins, their combined functions and their output priorities

are briefly described here. For additional information,

refer to the appropriate section in this data sheet.

When multiple outputs are enabled, the actual pin

control goes to the peripheral with the lowest number in

the following lists.

Analog input functions, such as ADC, comparator and

CapSense inputs, are not shown in the priority lists.

These inputs are active when the I/O pin is set for

Analog mode using the ANSELx registers. Digital

output functions may control the pin when it is in Analog

mode with the priority shown below.

RA0

AN0 (ADC)

SEG33 (LCD)

CPS0 (CSM)

RA1

SEG18

CPS1 (CSM)

RA2

SEG34 (LCD)

VREF- (DAC)

AN2 (ADC)

CPS2 (CSM)

RA3

VREF+ (DAC)

SEG35 (LCD)

AN3 (ADC)

CPS3 (CSM)

RA4

SEG14 (LCD)

T0CKI (TMR0)

RA5

AN4 (ADC)

SEG15 (LCD)

CPS4 (CSM)

RA6

OSC2 (enabled by Configuration Word)

CLKOUT (enabled by Configuration Word)

SEG36 (LCD)

RA7

OSC1/CLKIN (enabled by Configuration Word)

SEG37 (LCD)

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

B'11110000' ;Set RA<7:4> as inputs

MOVWF

TRISA

;and set RA<3:0> as

;outputs

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