PIC16F1934-ESLASHML datasheet(135/508 Pages) MICROCHIP

135 / 508 page

 2009 Microchip Technology Inc.

Preliminary

DS41364D-page 135

PIC16F193X/LF193X

12.3

PORTB Registers

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

corresponding data direction register is TRISB

(Register 12-7). 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., enable the output driver and

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

Example 12-2 shows how to initialize PORTB.

Reading the PORTB register (Register 12-6) reads the

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

PORT latch. All write operations are read-modify-write

operations. Therefore, a write to a port implies that the

port pins are read, this value is modified and then written

to the PORT data latch (LATB).

The TRISB register (Register 12-7) controls the PORTB

pin output drivers, even when they are being used as

analog inputs. The user should ensure the bits in the

TRISB register are maintained set when using them as

analog inputs. I/O pins configured as analog input always

read ‘0’.

12.3.1

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 (see Register 12-10). Each weak

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

configured as an output. All pull-ups are disabled on a

Power-on Reset by the WPUEN bit of the OPTION

12.3.2

INTERRUPT-ON-CHANGE

All of the PORTB pins are individually configurable as an

interrupt-on-change pin. Control bits IOCB<7:0> enable

or disable the interrupt function for each pin. The

interrupt-on-change feature is disabled on a Power-on

Reset.

Reference

Section 13.0

“Interrupt-On-Change”

for more information.

12.3.3

ANSELB REGISTER

The ANSELB register (Register 12-9) is used to

configure the Input mode of an I/O pin to analog.

Setting the appropriate ANSELB bit high will cause all

digital reads on the pin to be read as ‘0’ and allow

analog functions on the pin to operate correctly.

The state of the ANSELB bits has no affect on digital

output functions. A pin with TRIS clear and ANSELB set

will still operate as a digital output, but the Input mode

will be analog. This can cause unexpected behavior

when executing read-modify-write instructions on the

affected port.

EXAMPLE 12-2:

INITIALIZING PORTB

Note:

The ANSELB register must be initialized to

configure an analog channel as a digital

input. Pins configured as analog inputs will

read ‘0’.

BANKSEL PORTB

;

CLRF

PORTB

;Init PORTB

BANKSEL LATB

;Data Latch

CLRF

LATB

;

BANKSEL ANSELB

CLRF

ANSELB

;Make RB<7:0> digital

BANKSEL TRISB

;

MOVLW

’11110000’ ;Set RB<7:4> as inputs

;and RB<3:0> as outputs

MOVWF

TRISB

;

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