PIC16C71 datasheet(53/337 Pages) MICROCHIP

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DS30234D-page 53

PIC16C6X

5.2

PORTB and TRISB Register

PORTB is an 8-bit wide bi-directional port. The corre-

sponding data direction register is TRISB. Setting a bit

in the TRISB register puts the corresponding output

driver in a hi-impedance mode. Clearing a bit in the

TRISB register puts the contents of the output latch on

the selected pin(s).

EXAMPLE 5-2:

INITIALIZING PORTB

BCF

STATUS, RP0

;

CLRF

PORTB

; Initialize PORTB by

; clearing output

; data latches

BSF

STATUS, RP0

; Select Bank 1

MOVLW

0xCF

; Value used to

; initialize data

; direction

MOVWF

TRISB

; Set RB<3:0> as inputs

; RB<5:4> as outputs

; RB<7:6> as inputs

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 (OPTION<7>). The

weak pull-up is automatically turned off when the port

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

disabled on a Power-on Reset.

Four of PORTB’s pins, RB7:RB4, have an interrupt on

change feature. Only pins conﬁgured as inputs can

cause this interrupt to occur (i.e., any RB7:RB4 pin

conﬁgured as an output is excluded from the interrupt

on change comparison). The input pins (of RB7:RB4)

are compared with the old value latched on the last

read of PORTB. The “mismatch” outputs of RB7:RB4

are OR’ed together to generate the RB port change

interrupt with ﬂag bit RBIF (INTCON<0>).

Applicable Devices

61 62 62A R62 63 R63 64 64A R64 65 65A R65 66 67

This interrupt can wake the device from SLEEP. The

user, in the interrupt service routine, can clear the inter-

rupt in the following manner:

Any read or write of PORTB. This will end the

mismatch condition.

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.

This interrupt on mismatch feature, together with soft-

ware conﬁgurable pull-ups on these four pins allow

easy interface to a keypad and make it possible for

wake-up on key-depression. Refer to the Embedded

Control Handbook, Application Note,

“Implementing

Wake-up on Key Stroke” (AN552).

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.

FIGURE 5-3:

BLOCK DIAGRAM OF THE

RB7:RB4 PINS FOR

PIC16C61/62/64/65

Note:

For PIC16C61/62/64/65, if a change on the

I/O pin should occur when a read operation

is being executed (start of the Q2 cycle),

then interrupt ﬂag bit RBIF may not get set.

Data Latch

From other

RBPU(2)

VDD

I/O

Data bus

WR Port

WR TRIS

Set RBIF

TRIS Latch

RD TRIS

RD Port

RB7:RB4 pins

weak

pull-up

RD Port

Latch

TTL

Input

Buffer

pin(1)

Note 1: I/O pins have diode protection to VDD and VSS.

2: To enable weak pull-ups, set the appropriate TRIS bit(s)

and clear the RPBU bit (OPTION<7>).

Buffer

RB7:RB6 in serial programming mode

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