PIC16F753 datasheet(41/230 Pages) MICROCHIP

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DS40001709C-page 41

PIC16F753/HV753

5.3

PORTA and TRISA Registers

PORTA is a 6-bit wide port with five bidirectional and one

input-only pin. The corresponding data direction register

is TRISA (Register 5-2). 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 5-1 shows how to initialize PORTA.

Reading the PORTA register (Register 5-2) 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. RA3 reads ‘0’ when

MCLRE = 1.

The TRISA register controls the direction of the

PORTA pins, even when they are being used as analog

inputs. The user must ensure the bits in the TRISA

inputs. I/O pins configured as analog input always read

‘0’.

5.3.1

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 5-1.

When multiple outputs are enabled, the actual pin

control goes to the peripheral with the highest priority.

Analog input functions, such as comparator inputs, are

not shown in the priority lists. These inputs are active

when the peripheral is enabled and the input multiplexer

for the pin is selected. The Analog mode, set with the

ANSELA register, disables the digital input buffer

thereby preventing excessive input current when the

analog input voltage is between logic states. Digital

output functions may control the pin when it is in Analog

mode with the priority shown in Table 5-1.

Note:

The ANSEL register must be initialized to

configure an analog channel as a digital

input. Pins configured as analog inputs will

read ‘0’ and cannot generate an interrupt.

TABLE 5-1:

PORTA OUTPUT PRIORITY

Pin Name

Function Priority

RA0

ICSPDAT

FVROUT

DACOUT

C1IN0+

RA0

RA1

FVRIN

ICSPCLK

VREF+

C1IN0-

C2IN0-

RA1

RA2

COG1FLT

T0CKI

C1OUT

INT

RA2

RA3

MCLR

VPP

T1G

RA3

RA4

CLKOUT

T1G

RA4

RA5

CLKIN

T1CKI

RA5

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