PIC17C752 datasheet(68/320 Pages) MICROCHIP

68 / 320 page

PIC17C75X

DS30264A-page 68

Preliminary

10.2 PORTB and DDRB Registers

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

sponding data direction register is DDRB. A '1' in

DDRB conﬁgures the corresponding port pin as an

input. A '0' in the DDRB register conﬁgures the corre-

sponding port pin as an output. Reading PORTB reads

the status of the pins, whereas writing to it will write to

the port latch.

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

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

done by clearing the RBPU (PORTA<7>) bit. The weak

pull-up is automatically turned off when the port pin is

conﬁgured as an output. The pull-ups are enabled on

any reset.

PORTB also has an interrupt on change feature. Only

pins conﬁgured as inputs can cause this interrupt to

occur (i.e. any RB7:RB0 pin conﬁgured as an output is

excluded from the interrupt on change comparison).

The input pins (of RB7:RB0) are compared with the

value in the PORTB data latch. The “mismatch” outputs

of RB7:RB0 are OR’ed together to set the PORTB

Interrupt Flag bit, RBIF (PIR1<7>).

This interrupt can wake the device from SLEEP. The

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

rupt by:

Read-Write PORTB (such as; MOVPF PORTB,

PORTB

). This will end mismatch condition.

Then, clear the RBIF bit.

A mismatch condition will continue to set the RBIF bit.

Reading then writing PORTB will end the mismatch

condition, and allow the RBIF bit to be cleared.

This interrupt on mismatch feature, together with soft-

ware conﬁgurable pull-ups on this port, allows easy

interface to a keypad and make it possible for wake-up

on key-depression. For an example, refer to Applica-

tion Note AN552, “Implementing Wake-up on Key-

stroke.”

The interrupt on change feature is recommended for

wake-up on operations where PORTB is only used for

the interrupt on change feature and key depression

operations.

FIGURE 10-5: BLOCK DIAGRAM OF RB5:RB4 AND RB1:RB0 PORT PINS

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

Data Bus

Weak

Pull-Up

Port

Input Latch

Port

Data

WR_PORTB (Q4)

WR_DDRB (Q4)

RD_PORTB (Q2)

RD_DDRB (Q2)

RBIF

RBPU

Match Signal

from other

port pins

(PORTA<7>)

Peripheral Data in

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