PIC16F1507-ESLASHSS. datasheet(97/278 Pages) MICROCHIP

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DS40001586D-page 97

PIC16(L)F1507

11.3

PORTA Registers

11.3.1

DATA REGISTER

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

corresponding data direction register is TRISA

(Register 11-3). 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). The exception is RA3, which is

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

Example 11-1 shows how to initialize an I/O port.

Reading the PORTA register (Register 11-2) 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).

11.3.2

DIRECTION CONTROL

The TRISA register (Register 11-3) 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’.

11.3.3

ANALOG CONTROL

The ANSELA register (Register 11-5) 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.

EXAMPLE 11-1:

INITIALIZING PORTA

11.3.4

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 11-2.

When multiple outputs are enabled, the actual pin

control goes to the peripheral with the highest priority.

Analog input functions, such as ADC and comparator

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 in Table 11-2.

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.

BANKSEL

PORTA

;

CLRF

PORTA

;Init PORTA

BANKSEL

LATA

;Data Latch

CLRF

LATA

;

BANKSEL

ANSELA

;

CLRF

ANSELA

;digital I/O

BANKSEL

TRISA

;

MOVLW

B'00111000' ;Set RA<5:3> as inputs

MOVWF

TRISA

;and set RA<2:0> as

;outputs

TABLE 11-2:

PORTA OUTPUT PRIORITY

Pin Name

Function Priority(1)

RA0

ICSPDAT

RA0

RA1

RA2

CLC1(2)

PWM3

RA2

RA3

None

RA4

CLKOUT

RA4

RA5

Note

Priority listed from highest to lowest.

Default pin (see APFCON register).

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