PIC16F87 datasheet(51/230 Pages) MICROCHIP

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 2002-2013 Microchip Technology Inc.

DS30487D-page 51

PIC16F87/88

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

“PIC® Mid-Range MCU Family Reference Manual”

(DS33023).

5.1

PORTA and the TRISA Register

PORTA is an 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. 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. On PIC16F88 devices, it is also multiplexed with

an analog input to become the RA4/AN4/T0CKI/

C2OUT pin. The RA4/AN4/T0CKI/C2OUT pin is a

Schmitt Trigger input and full CMOS output driver.

Pin RA5 is multiplexed with the Master Clear module

input. The RA5/MCLR/VPP pin is a Schmitt Trigger

input.

Pin RA6 is multiplexed with the oscillator module input

and external oscillator output. Pin RA7 is multiplexed

with the oscillator module input and external oscillator

input. Pin RA6/OSC2/CLKO and pin RA7/OSC1/CLKI

are Schmitt Trigger inputs and full CMOS output drivers.

Pins RA<1:0> are multiplexed with analog inputs. Pins

RA<3:2> are multiplexed with analog inputs and com-

parator outputs. On PIC16F88 devices, pins RA<3:2>

are also multiplexed with the VREF inputs. Pins RA<3:0>

have TTL inputs and full CMOS output drivers.

EXAMPLE 5-1:

INITIALIZING PORTA

TABLE 5-1:

PORTA FUNCTIONS

Note:

Power-on

Reset,

the

pins

PORTA<4:0> are configured as analog

inputs and read as ‘0’.

BANKSEL PORTA

; select bank of PORTA

CLRF

PORTA

; Initialize PORTA by

; clearing output

; data latches

BANKSEL ANSEL

; Select Bank of ANSEL

MOVLW

0x00

; Configure all pins

MOVWF

ANSEL

; as digital inputs

MOVLW

0xFF

; Value used to

; initialize data

; direction

MOVWF

TRISA

; Set RA<7:0> as inputs

Name

Bit#

Buffer

Function

RA0/AN0

bit 0

TTL

Input/output or analog input.

RA1/AN1

bit 1

TTL

Input/output or analog input.

RA2/AN2/CVREF/VREF-(2)

bit 2

TTL

Input/output, analog input, VREF- or comparator VREF

output.

RA3/AN3/VREF+(2)/C1OUT

bit 3

TTL

Input/output, analog input, VREF+ or comparator output.

RA4/AN4(2)/T0CKI/C2OUT

bit 4

Input/output, analog input, TMR0 external input or

comparator output.

RA5/MCLR/VPP

bit 5

Input, Master Clear (Reset) or programming voltage input.

RA6/OSC2/CLKO

bit 6

Input/output, connects to crystal or resonator, oscillator

output or 1/4 the frequency of OSC1 and denotes the

instruction cycle in RC mode.

RA7/OSC1/CLKI

bit 7

ST/CMOS(1) Input/output, connects to crystal or resonator or oscillator

input.

Legend: TTL = TTL input, ST = Schmitt Trigger input

Note 1:

This buffer is a Schmitt Trigger input when configured in RC Oscillator mode and a CMOS input otherwise.

PIC16F88 only.

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