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2004 Microchip Technology Inc.

DS30498C-page 49

PIC16F7X7

5.0

I/O PORTS

Some pins for these I/O ports are multiplexed with an

alternate function for the peripheral features on the

device. In general, when a peripheral is enabled, that

pin may not be used as a general purpose I/O pin.

Additional information on I/O ports may be found in the

“PICmicro

Mid-Range

MCU

Family

Reference

Manual” (DS33023).

5.1

PORTA and the TRISA Register

PORTA is a 8-bit wide, bidirectional port. The corre-

sponding data direction register is TRISA. Setting a

TRISA bit (= 1) will make the corresponding PORTA pin

an input (i.e., put the corresponding output driver in a

high-impedance mode). Clearing a TRISA bit (= 0) will

make the corresponding PORTA pin an output (i.e., put

the contents of the output latch on the selected pin).

Reading the PORTA register reads the status of the

pins, whereas writing to it, will write to the port latch.

The RA4 pin is multiplexed with the Timer0 module

clock input and one of the comparator outputs to

become the RA4/T0CKI/C1OUT pin. Pins RA6 and

RA7 are multiplexed with the main oscillator pins; they

are enabled as oscillator or I/O pins by the selection of

the main oscillator in Configuration Register 1H (see

Section 15.1 “Configuration Bits” for details). When

they are not used as port pins, RA6 and RA7 and their

associated TRIS and LAT bits are read as ‘0’.

The other PORTA pins are multiplexed with analog

inputs, the analog VREF+ and VREF- inputs and the

comparator voltage reference output. The operation of

pins RA3:RA0 and RA5 as A/D converter inputs is

selected by clearing/setting the control bits in the

ADCON1 register (A/D Control Register 1). Pins RA0

through RA5 may also be used as comparator inputs or

outputs by setting the appropriate bits in the CMCON

The RA4/T0CKI/C1OUT pin is a Schmitt Trigger input

and an open-drain output. All other PORTA pins have

TTL input levels and full CMOS output drivers.

The TRISA register controls the direction of the RA pins

even when they are being used as analog inputs. The

user must ensure the bits in the TRISA register are

maintained set when using them as analog inputs.

EXAMPLE 5-1:

INITIALIZING PORTA

Note:

On a Power-on Reset, RA5 and RA3:RA0

are configured as analog inputs and read

as ‘0’. RA4 is configured as a digital input.

BCF

STATUS, RP0

;

BCF

STATUS, RP1

; Bank0

CLRF

PORTA

; Initialize PORTA by

; clearing output

; data latches

BSF

STATUS, RP0

; Select Bank 1

MOVLW

0x0F

; Configure all pins

MOVWF

ADCON1

; as digital inputs

MOVLW

0xCF

; Value used to

; initialize data

; direction

MOVWF

TRISA

; Set RA<3:0> as inputs

; RA<5:4> as outputs

; TRISA<7:6>are always

; read as '0'.

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