PIC16CE623 datasheet(23/114 Pages) MICROCHIP

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DS40182D-page 23

PIC16CE62X

5.0

I/O PORTS

The PIC16CE62X parts 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 a 5-bit wide latch. RA4 is a Schmitt Trigger input

and an open drain output. Port RA4 is multiplexed with the

T0CKI clock input. 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 con-

figure these pins as input or output.

A '1' in the TRISA register puts the corresponding output

driver in a hi- impedance mode. A '0' 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. 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

and

the

VRCON (Voltage Reference Control Register) register.

When selected as a comparator input, these pins will

read as '0's.

FIGURE 5-1:

BLOCK DIAGRAM OF

RA<1:0> PINS

Data

Bus

PortA

TRISA

Data Latch

TRIS Latch

RD TRISA

RD PORTA

Analog

VSS

VDD

I/O Pin

Input Mode

To Comparator

Schmitt Trigger

Input Buffer

VDD

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 VREF 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

FIGURE 5-2:

BLOCK DIAGRAM OF RA2 PIN

Note:

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 excess current consumption.

CLRF

PORTA

;Initialize PORTA by setting

;output data latches

MOVLW 0X07

;Turn comparators off and

MOVWF CMCON

;enable pins for I/O

;functions

BSF

STATUS, RP0 ;Select Bank1

MOVLW 0x1F

;Value used to initialize

;data direction

MOVWF TRISA

;Set RA<4:0> as inputs

;TRISA<7:5> are always

;read as '0'.

Data

Bus

PortA

TRISA

Data Latch

TRIS Latch

RD TRISA

RD PORTA

Analog

VSS

VDD

RA2 Pin

Input Mode

To Comparator

Schmitt Trigger

Input Buffer

VROE

VREF

VDD

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