PIC16F917ESLASHML301 datasheet(43/272 Pages) MICROCHIP

43 / 272 page

Preliminary

DS41250E-page 41

PIC16F917/916/914/913

3.2

PORTB and TRISB Registers

PORTB is a general purpose I/O port with similar

functionality as the PIC16F77. All PORTB pins can have

a weak pull-up feature, and PORTB<7:4> implements an

interrupt-on-input change function.

PORTB is also used for the Serial Flash programming

interface.

EXAMPLE 3-2:

INITIALIZING PORTB

3.3

Additional PORTB Pin Functions

RB<7:6> are used as data and clock signals, respectively,

for both serial programming and the in-circuit debugger

features on the device. Also, RB0 can be configured as an

external interrupt input.

3.3.1

WEAK PULL-UPS

Each of the PORTB pins has an individually configurable

internal weak pull-up. Control bits WPUB<7:0> enable or

disable each pull-up. Refer to Register 3-6. Each 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 by the RBPU bit (OPTION_REG<7>).

3.3.2

INTERRUPT-ON-CHANGE

Four of the PORTB pins are individually configurable

as an interrupt-on-change pin. Control bits IOCB<7:4>

enable or disable the interrupt function for each pin.

Refer to Register 3-5. The interrupt-on-change feature

is disabled on a Power-on Reset.

For enabled interrupt-on-change pins, the values are

compared with the old value latched on the last read of

PORTB. The ‘mismatch’ outputs of the last read are

OR’d together to set the PORTB Change Interrupt flag

bit (RBIF) in the INTCON register (Register 2-3).

This interrupt can wake the device from Sleep. The user,

in the Interrupt Service Routine, clears the interrupt by:

Any read or write of PORTB. This will end the

mismatch condition.

Clear the flag bit RBIF.

A mismatch condition will continue to set flag bit RBIF.

Reading or writing PORTB will end the mismatch con-

dition and allow flag bit RBIF to be cleared. The latch

holding the last read value is not affected by a MCLR

nor Brown-out Reset. After these Resets, the RBIF flag

will continue to be set if a mismatch is present.

Note:

Analog lines that carry LCD signals

(i.e., SEGx, COMy, where x and y are seg-

ment and common identifiers) are shown

as direct connections to the device pins.

The signals are outputs from the LCD

module and may be tri-stated, depending

on the configuration of the LCD module.

BCF

STATUS,RP0 ;Bank 0

BCF

STATUS,RP1 ;

CLRF

PORTB

;Init PORTB

BSF

STATUS,RP0 ;Bank 1

BCF

STATUS,RP1 ;

MOVLW

FFh

;Set RB<7:0> as inputs

MOVWF

TRISB

;

BCF

STATUS,RP0 ;Bank 0

BCF

STATUS,RP1 ;

Note:

If a change on the I/O pin should occur

when the read operation is being executed

(start of the Q2 cycle), then the RBIF

interrupt flag may not get set. Furthermore,

since a read or write on a port affects all bits

of that port, care must be taken when using

multiple pins in Interrupt-on-change mode.

Changes on one pin may not be seen while

servicing changes on another pin.

PIC16F917E/ML301 Datasheet(PDF) 43 Page - Microchip Technology

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