INTEDG datasheet(127/478 Pages) MICROCHIP

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 2010-2012 Microchip Technology Inc.

DS41414D-page 127

PIC16(L)F1946/47

12.0 I/O PORTS

Each port has three standard registers for its operation.

These registers are:

• TRISx registers (data direction)

• PORTx registers (reads the levels on the pins of

the device)

• LATx registers (output latch)

Some ports may have one or more of the following

additional registers. These registers are:

• ANSELx (analog select)

• WPUx (weak pull-up)

In general, when a peripheral is enabled on a port pin,

that pin cannot be used as a general purpose output.

However, the pin can still be read.

The Data Latch (LATx registers) is useful for

read-modify-write operations on the value that the I/O

pins are driving.

A write operation to the LATx register has the same

effect as a write to the corresponding PORTx register.

A read of the LATx register reads of the values held in

the I/O PORT latches, while a read of the PORTx

Ports that support analog inputs have an associated

ANSELx register. When an ANSEL bit is set, the digital

input buffer associated with that bit is disabled.

Disabling the input buffer prevents analog signal levels

on the pin between a logic high and low from causing

excessive current in the logic input circuitry. A

simplified model of a generic I/O port, without the

interfaces to other peripherals, is shown in Figure 12-1.

FIGURE 12-1:

GENERIC I/O PORT

OPERATION

EXAMPLE 12-1:

INITIALIZING PORTA

TABLE 12-1:

PORT AVAILABILITY PER

DEVICE

Device

PIC16F1946

●●

PIC16F1947

●●●

Write LATx

Data Register

I/O pin

Read PORTx

Write PORTx

TRISx

Read LATx

Data Bus

To peripherals

ANSELx

VDD

VSS

; This code example illustrates

; initializing the PORTA register. The

; other ports are initialized in the same

; manner.

BANKSEL PORTA

;

CLRF

PORTA

;Init PORTA

BANKSEL LATA

;Data Latch

CLRF

LATA

;

BANKSEL ANSELA

;

CLRF

ANSELA

;digital I/O

BANKSEL TRISA

;

MOVLW

B'00111000' ;Set RA<5:3> as inputs

MOVWF

TRISA

;and set RA<2:0> as

;outputs

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