PIC16 datasheet(115/418 Pages) MICROCHIP

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 2011-2013 Microchip Technology Inc.

DS40001609C-page 115

PIC16(L)F1508/9

11.5

PORTB Registers

11.5.1

DATA REGISTER

PORTB is a 4-bit wide, bidirectional port. The

corresponding data direction register is TRISB

(Register 11-8). Setting a TRISB bit (= 1) will make the

corresponding PORTB pin an input (i.e., disable the

output driver). Clearing a TRISB bit (= 0) will make the

corresponding PORTB pin an output (i.e., enables

output driver and puts the contents of the output latch

on the selected pin). Example 11-1 shows how to

initialize an I/O port.

Reading the PORTB register (Register 11-7) 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).

11.5.2

DIRECTION CONTROL

The TRISB register (Register 11-8) 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’.

11.5.3

ANALOG CONTROL

The ANSELB register (Register 11-10) 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 effect on digital

output functions. A pin with TRIS clear and ANSEL 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.

11.5.4

PORTB FUNCTIONS AND OUTPUT

PRIORITIES

Each PORTB pin is multiplexed with other functions. The

pins, their combined functions and their output priorities

are shown in Table 11-5.

When multiple outputs are enabled, the actual pin

control goes to the peripheral with the highest priority.

Analog input functions, such as ADC and comparator

inputs, are not shown in the priority lists. These inputs

are active when the I/O pin is set for Analog mode using

the ANSELx registers. Digital output functions may

control the pin when it is in Analog mode with the

priority shown below in Table 11-5.

Note:

The ANSELB bits default to the Analog

mode after Reset. To use any pins as

digital general purpose or peripheral

inputs, the corresponding ANSEL bits

must be initialized to ‘0’ by user software.

TABLE 11-5:

PORTB OUTPUT PRIORITY

Pin Name

Function Priority(1)

RB4

SDA

RB4

RB5

RB6

SCL

SCK

RB6

RB7

CLC3

RB7

Note 1: Priority listed from highest to lowest.

Default pin (see APFCON register).

Alternate pin (see APFCON register).

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