PIC16C71-04SLASHP datasheet(25/176 Pages) MICROCHIP

25 / 176 page

DS30272A-page 25

PIC16C71X

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.

5.1

PORTA and TRISA Registers

PORTA is a 5-bit latch.

The RA4/T0CKI pin is a Schmitt Trigger input and an

open drain output. All other RA port pins have TTL

input levels and full CMOS output drivers. All pins have

data direction bits (TRIS registers) which can conﬁgure

these pins as output or input.

Setting a TRISA register bit puts the corresponding out-

put driver in a hi-impedance mode. Clearing a bit in the

TRISA register puts the contents of the output latch on

the selected pin(s).

Reading the PORTA register 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.

Pin RA4 is multiplexed with the Timer0 module clock

input to become the RA4/T0CKI pin.

Other PORTA pins are multiplexed with analog inputs

and analog VREF input. The operation of each pin is

selected by clearing/setting the control bits in the

ADCON1 register (A/D Control Register1).

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

BCF

STATUS, RP0

;

CLRF

PORTA

; Initialize PORTA by

; clearing output

; data latches

BSF

STATUS, RP0

; Select Bank 1

MOVLW

0xCF

; Value used to

; initialize data

; direction

MOVWF

TRISA

; Set RA<3:0> as inputs

; RA<4> as outputs

; TRISA<7:5> are always

; read as '0'.

Applicable Devices

710 71 711 715

Note:

On a Power-on Reset, these pins are con-

ﬁgured as analog inputs and read as '0'.

FIGURE 5-1:

BLOCK DIAGRAM OF

RA3:RA0 PINS

FIGURE 5-2:

BLOCK DIAGRAM OF RA4/

T0CKI PIN

Data

bus

Port

TRIS

Data Latch

TRIS Latch

RD TRIS

RD PORT

VSS

VDD

I/O pin(1)

Note 1:

I/O pins have protection diodes to VDD and

VSS.

Analog

input

mode

TTL

input

buffer

To A/D Converter

Data

bus

PORT

TRIS

RD PORT

Data Latch

TRIS Latch

RD TRIS

Schmitt

Trigger

input

buffer

VSS

I/O pin(1)

TMR0 clock input

Note 1: I/O pin has protection diodes to VSS only.

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