PIC18F83J11T-I/PT【PDF 38/332 页】IC PIC MCU FLASH 4KX16 80TQFP

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PIC18F85J11 FAMILY

DS39774D-page 132

2010 Microchip Technology Inc.

11.3

PORTB, TRISB and

LATB Registers

PORTB is an 8-bit wide, bidirectional port. The corre-

sponding Data Direction and Output Latch registers are

TRISB and LATB. All pins on PORTB are digital only

and tolerate voltages up to 5.5V.

Each of the PORTB pins has a weak internal pull-up. A

single control bit can turn on all the pull-ups. This is

performed by clearing bit RBPU (INTCON2<7>). The

weak pull-up is automatically turned off when the port

pin is configured as an output. The pull-ups are

disabled on a Power-on Reset.

Four of the PORTB pins (RB<7:4>) have an

interrupt-on-change feature. Only pins configured as

inputs can cause this interrupt to occur (i.e., any

RB<7:4> pin configured as an output is excluded from

the interrupt-on-change comparison). The input pins (of

RB<7:4>) are compared with the old value latched on

the last read of PORTB. The “mismatch” outputs of

RB<7:4> are ORed together to generate the RB Port

Change Interrupt with Flag bit, RBIF (INTCON<0>).

This interrupt can wake the device from power-managed

modes. The user, in the Interrupt Service Routine, can

clear the interrupt in the following manner:

Any read or write of PORTB (except with the

MOVFF

(ANY),

PORTB

instruction). This will

end the mismatch condition.

Wait one instruction cycle (such as executing a

NOP

instruction).

Clear flag bit, RBIF.

A mismatch condition will continue to set flag bit, RBIF.

Reading PORTB will end the mismatch condition and

allow flag bit, RBIF, to be cleared after one TCY delay.

The interrupt-on-change feature is recommended for

wake-up on key depression operation and operations

where PORTB is only used for the interrupt-on-change

feature. Polling of PORTB is not recommended while

using the interrupt-on-change feature.

EXAMPLE 11-2:

INITIALIZING PORTB

CLRF

PORTB

; Initialize PORTB by

; clearing output

; data latches

CLRF

LATB

; Alternate method

; to clear output

; data latches

MOVLW

0CFh

; Value used to

; initialize data

; direction

MOVWF

TRISB

; Set RB<3:0> as inputs

; RB<5:4> as outputs

; RB<7:6> as inputs

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