PIC16F1847_13 Datasheet, PDF (125/440 Pages) Microchip Technology – 18/20/28-Pin Flash Microcontrollers with XLP Technology

12.5 PORTB and TRISB Registers
12.5.1 DATA REGISTER
PORTB is an 8-bit wide, bidirectional port. The
corresponding data direction register is TRISB
(Register 12-9). 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 12-8) 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.
12.5.2 DIRECTION CONTROL
The TRISB register (Register 12-9) 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’. Example 12-2 shows how to initialize PORTB.
EXAMPLE 12-2: INITIALIZING PORTB
BANKSEL PORTB
;
CLRF PORTB
;Init PORTB
BANKSEL ANSELB
CLRF ANSELB
;Make RB<7:0> digital
BANKSEL TRISB
;
MOVLW B’11110000’ ;Set RB<7:4> as inputs
;and RB<3:0> as outputs
MOVWF TRISB
;
12.5.3 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.
12.5.4 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 12-11). 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_REG
register.
PIC16(L)F1847
12.5.5 ANALOG CONTROL
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
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.
The TRISB register (Register 12-9) 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’.
Note:
The ANSELB register must be initialized
to configure an analog channel as a digital
input. Pins configured as analog inputs
will read ‘0’.
 2011-2013 Microchip Technology Inc.
Preliminary
DS40001453D-page 125