PIC16F1934-ESLASHML datasheet(131/508 Pages) MICROCHIP

131 / 508 page

 2009 Microchip Technology Inc.

Preliminary

DS41364D-page 131

PIC16F193X/LF193X

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 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’.

12.2.1

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 affect 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 12-1:

INITIALIZING PORTA

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 briefly described here. For additional information,

refer to the appropriate section in this data sheet.

When multiple outputs are enabled, the actual pin

control goes to the peripheral with the lowest number in

the following lists.

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 shown below.

RA0

VCAP (enabled by Configuration Word)

SEG12 (LCD)

SRNQ (SR Latch)

C2OUT (Comparator)

RA0

RA1

SEG7 (LCD)

RA1

RA2

COM2 (LCD)

DACOUT (DAC)

RA2

RA3

COM3 (LCD), 28-pin only

SEG15 (LCD)

RA3

RA4

SEG4 (LCD)

SRQ (SR Latch)

C1OUT (Comparator)

CCP5 (CCP), 28-pin only

RA4

RA5

VCAP (enabled by Configuration Word)

SEG5 (LCD)

SRNQ (SR Latch)

C2OUT (Comparator)

RA5

RA6

VCAP (enabled by Configuration Word)

OSC2 (enabled by Configuration Word)

CLKOUT (enabled by Configuration Word)

SEG1 (LCD)

RA6

RA7

OSC1/CLKIN (enabled by Configuration Word)

SEG2 (LCD)

RA7

Note:

The ANSELA register must be initialized to

configure an analog channel as a digital

input. Pins configured as analog inputs will

read ‘0’.

BANKSEL

PORTA

;

CLRF

PORTA

;Init PORTA

BANKSEL

LATA

;Data Latch

CLRF

LATA

;

BANKSEL

ANSELA

;

CLRF

ANSELA

;digital I/O

BANKSEL

TRISA

;

MOVLW

B'11110000' ;Set RA<7:4> as inputs

MOVWF

TRISA

;and set RA<3:0> as

;outputs

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