PIC16F1526 datasheet(119/354 Pages) MICROCHIP

119 / 354 page

 2011 Microchip Technology Inc.

Preliminary

DS41458A-page 119

PIC16(L)F1526/27

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 an I/O port.

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 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.

12.2.2

PORTA FUNCTIONS AND OUTPUT

PRIORITIES

Each PORTA pin is multiplexed with other functions. The

pins, their combined functions and their output priorities

are 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, 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 in Table 12-2.

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

Pin Name

Function Priority(1)

RA0

RA1

RA2

RA3

RA4

RA5

RA6

CLKOUT

OSC2

RA6

RA7

Note 1:

Priority listed from highest to lowest.

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