PIC16F1946 datasheet(130/478 Pages) MICROCHIP

130 / 478 page

PIC16(L)F1946/47

DS41414D-page 130

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12.3

PORTA Registers

PORTA is an 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’.

12.3.1

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 effect 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.

12.3.2

PORTA FUNCTIONS AND OUTPUT

PRIORITIES

Each PORTA pin is multiplexed with other functions. The

pins, their combined functions and their output priorities

are shown in Table 12-2.

When multiple outputs are enabled, the actual pin

control goes to the peripheral with the highest priority.

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 list.

Note:

The ANSELA bits default to the Analog

mode after Reset. To use any pins as

digital general purpose or peripheral

inputs, the corresponding ANSEL bits

must be initialized to ‘0’ by user software.

TABLE 12-2:

PORTA OUTPUT PRIORITY

Name

Function Priority(1)

RA0

SEG33 (LCD)

RA0

RA1

SEG18

RA1

RA2

SEG34 (LCD)

RA2

RA3

SEG35 (LCD)

RA3

RA4

SEG14 (LCD)

RA4

RA5

SEG15 (LCD)

RA5

RA6

OSC2 (enabled by Configuration Word)

CLKOUT (enabled by Configuration Word)

SEG36 (LCD)

RA6

RA7

OSC1/CLKIN (enabled by Configuration

Word)

SEG37 (LCD)

RA7

Note 1: Priority listed from highest to lowest.

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