16F1829 datasheet(133/420 Pages) MICROCHIP

133 / 420 page

 2010 Microchip Technology Inc.

Preliminary

DS41440A-page 133

PIC16F/LF1825/1829

12.3

PORTB Registers

(PIC16F/LF1829 only)

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

corresponding data direction register is TRISB

(Register 12-10). 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 12-9) 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 12-10) 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’.

The INLVLB register (Register 12-14) controls the input

voltage threshold for each of the available PORTB

input pins. A selection between the Schmitt Trigger

CMOS or the TTL Compatible thresholds is available.

The input threshold is important in determining the

value of a read of the PORTB register and also the level

at which an Interrupt-on-Change occurs, if that feature

is enabled. See Section 30.4 “DC Characteristics:

PIC16F/LF1825/1829-I/E” for more information on

threshold levels.

12.3.1

ANSELB REGISTER

The ANSELB register (Register 12-12) 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 out-

put 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 exe-

cuting read-modify-write instructions on the affected

port.

EXAMPLE 12-2:

INITIALIZING PORTB

Note:

Changing the input threshold selection

should be performed while all peripheral

modules are disabled. Changing the

threshold level during the time a module is

active may inadvertently generate a tran-

sition associated with an input pin, regard-

less of the actual voltage level on that pin.

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<7:4> digital

BANKSEL TRISB

;

MOVLW

B’00110000’;Set RB<5:4> as inputs

;and RB<3:0> as outputs

MOVWF

TRISB

;

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