PIC16F913/914/916/917/946
3.3
PORTB and TRISB Registers
3.4
Additional PORTB Pin Functions
PORTB is an 8-bit bidirectional I/O port. All PORTB pins
can have a weak pull-up feature, and PORTB<7:4>
implements an interrupt-on-input change function.
RB<7:6> are used as data and clock signals, respectively,
for both serial programming and the in-circuit debugger
features on the device. Also, RB0 can be configured as an
external interrupt input.
PORTB is also used for the Serial Flash programming
interface and ICD interface.
3.4.1
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. Refer to Register 3-7. Each weak
pull-up is automatically turned off when the port pin is
configured as an output. The pull-ups are disabled on a
Power-on Reset by the RBPU bit of the OPTION
register.
EXAMPLE 3-2:
INITIALIZING PORTB
BANKSELPORTB
;
CLRF
PORTB
;Init PORTB
;
;Set RB<7:0> as inputs
;
BANKSELTRISB
MOVLW
MOVWF
0FFh
TRISB
3.4.2
INTERRUPT-ON-CHANGE
Four of the PORTB pins are individually configurable
as an interrupt-on-change pin. Control bits IOCB<7:4>
enable or disable the interrupt function for each pin.
Refer to Register 3-6. The interrupt-on-change feature
is disabled on a Power-on Reset.
For enabled interrupt-on-change pins, the values are
compared with the old value latched on the last read of
PORTB. The ‘mismatch’ outputs of the last read are
OR’d together to set the PORTB Change Interrupt flag
bit (RBIF) in the INTCON register (Register 2-3).
This interrupt can wake the device from Sleep. The user,
in the Interrupt Service Routine, clears the interrupt by:
a) Any read or write of PORTB. This will end the
mismatch condition.
b) Clear the flag bit RBIF.
A mismatch condition will continue to set flag bit RBIF.
Reading or writing PORTB will end the mismatch con-
dition and allow flag bit RBIF to be cleared. The latch
holding the last read value is not affected by a MCLR
nor Brown-out Reset. After these Resets, the RBIF flag
will continue to be set if a mismatch is present.
Note:
If a change on the I/O pin should occur
when the read operation is being executed
(start of the Q2 cycle), then the RBIF
interrupt flag may not get set. Furthermore,
since a read or write on a port affects all bits
of that port, care must be taken when using
multiple pins in Interrupt-on-change mode.
Changes on one pin may not be seen while
servicing changes on another pin.
© 2007 Microchip Technology Inc.
DS41250F-page 53
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