PIC16F193X Datasheet, PDF (91/418 Pages) Microchip Technology – 28/40/44-Pin Flash-Based, 8-Bit CMOS Microcontrollers with LCD Driver and nanoWatt Technology

6.3 PORTB and TRISB Registers
PORTB is an 8-bit wide, bidirectional port. The
corresponding data direction register is TRISB
(Register 6-9). 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 6-2 shows how to initialize PORTB.
Reading the PORTB register (Register 6-6) 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.
The TRISB register (Register 6-9) 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 6-2 shows how to initialize PORTB.
EXAMPLE 6-2: 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
;
PIC16F193X/LF193X
6.3.1 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 6-8). 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
register.
6.3.2 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 7.0 “Interrupt-On-Change”
for more information.
Note:
The ANSELB register must be initialized to
configure an analog channel as a digital
input. Pins configured as analog inputs will
read ‘0’.
© 2008 Microchip Technology Inc.
Preliminary
DS41364A-page 89