PIC16F627-04/P【PDF 96/170 页】IC MCU FLASH 1KX14 COMP 18DIP

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Sheet目录3873

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2003 Microchip Technology Inc.

Preliminary

DS40300C-page 29

PIC16F62X

5.0

I/O PORTS

The PIC16F62X have two ports, PORTA and PORTB.

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 an 8-bit wide latch. RA4 is a Schmitt Trigger

input and an open drain output. Port RA4 is multiplexed

with the T0CKI clock input. RA5 is a Schmitt Trigger

input only and has no output drivers. All other RA port

pins have Schmitt Trigger input levels and full CMOS

output drivers. All pins have data direction bits (TRIS

registers) which can configure these pins as input or

output.

A '1' in the TRISA register puts the corresponding out-

put driver in a Hi-impedance mode. A '0' in the TRISA

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. So a

write to a port implies that the port pins are first read,

then this value is modified and written to the port data

latch.

The PORTA pins are multiplexed with comparator and

voltage reference functions. The operation of these

pins are selected by control bits in the CMCON

(comparator control register) register and the VRCON

(voltage reference control register) register. When

selected as a comparator input, these pins will read

as '0's.

TRISA controls the direction of the RA pins, even when

they are being used as comparator inputs. The user

must make sure to keep the pins configured as inputs

when using them as comparator inputs.

The RA2 pin will also function as the output for the

voltage reference. When in this mode, the V

REF pin is a

very high impedance output. The user must configure

TRISA<2> bit as an input and use high impedance

loads.

In one of the Comparator modes defined by the

CMCON register, pins RA3 and RA4 become outputs

of the comparators. The TRISA<4:3> bits must be

cleared to enable outputs to use this function.

EXAMPLE 5-1:

Initializing PORTA

CLRF

PORTA

;Initialize PORTA by

;setting output data latches

MOVLW 0x07

;Turn comparators off and

MOVWF CMCON

;enable pins for I/O

;functions

BCF

STATUS, RP1

BSF

STATUS, RP0;Select Bank1

MOVLW 0x1F

;Value used to initialize

;data direction

MOVWF TRISA

;Set RA<4:0> as inputs

;TRISA<5> always

;read as ‘1’.

;TRISA<7:6>

;depend on oscillator mode

Note:

RA5 shares function with V

PP. When VPP

voltage levels are applied to RA5, the

device will enter Programming mode.

Note 1: On RESET, the TRISA register is set to all

inputs. The digital inputs are disabled and

the comparator inputs are forced to

ground to reduce current consumption.

2: TRISA<6:7> is overridden by oscillator

configuration.

When

PORTA<6:7>

overridden, the data reads ‘0’ and the

TRISA<6:7> bits are ignored.

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