PIC12F752 datasheet(47/204 Pages) MICROCHIP

47 / 204 page

 2011 Microchip Technology Inc.

Preliminary

DS41576A-page 47

PIC12F752/HV752

5.3

PORTA and the TRISA Registers

PORTA is a 6-bit wide port with 5 bidirectional and 1

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 I/O pin is set for Analog mode using the

ANSELA registers. 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(1)

RA0

ICSPDAT

REFOUT

DACOUT

COG1OUT1(2)

RA0

RA1

RA2

COG1OUT0(2)

C1OUT

C2OUT

CCP1

RA2

RA3

None

RA4

CLKOUT

COG1OUT1(3)

RA4

RA5

COG1OUT0(3)

RA5

Note

Priority listed from highest to lowest.

Default function pin (see APFCON register).

Alternate function pin (see APFCON register).

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