PIC16F1933-I/ML【PDF 22/92 页】IC MCU 8BIT FLASH 28-QFN

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PIC18F2480/2580/4480/4580

DS39637D-page 138

2009 Microchip Technology Inc.

11.2

PORTB, TRISB and LATB

Registers

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

sponding Data Direction register is TRISB. Setting a

TRISB bit (= 1) will make the corresponding PORTB

pin an input (i.e., put the corresponding output driver in

a high-impedance mode). Clearing a TRISB bit (= 0)

will make the corresponding PORTB pin an output (i.e.,

put the contents of the output latch on the selected pin).

The Output Latch register (LATB) is also memory

mapped. Read-modify-write operations on the LATB

PORTB.

Pins, RB2 through RB3, are multiplexed with the ECAN

peripheral. Refer to Section 24.0 “ECAN Module” for

proper settings of TRISB when CAN is enabled.

EXAMPLE 11-2:

INITIALIZING PORTB

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 all device resets.

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 Sleep. The

user, in the Interrupt Service Routine, can clear the

interrupt in the following manner:

a) Any read or write of PORTB (except with the

MOVFF (ANY), PORTB instruction). This will

end the mismatch condition.

b) 1 TCY.

Clear flag bit, RBIF.

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

Reading PORTB and waiting 1 TCY will end the

mismatch condition and allow flag bit, RBIF, to be

cleared.

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.

Note:

On a Power-on Reset, RB4, RB1 and RB0

are configured as analog inputs by default

and read as ‘0’; RB<7:5> and RB<3:2>

are configured as digital inputs.

CLRF

PORTB

; Initialize PORTB by

; clearing output

; data latches

CLRF

LATB

; Alternate method

; to clear output

; data latches

MOVLW

0Eh

; Set RB<4:0> as

MOVWF

ADCON1 ; digital I/O pins

; (required if config bit

; PBADEN is set)

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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