PIC16C770 Microchip Technology Inc., PIC16C770 Datasheet - Page 35

• Manufacturer Part Number: PIC16C770
• Description: 18/20-pin, 8-bit Cmos Microcontrollers With 10/12-bit A/d
• Manufacturer: Microchip Technology Inc.

3.3
PORTB is an 8-bit wide bi-directional port. The corre-
sponding data direction register is TRISB. Setting a
TRISB bit (=1) will make the corresponding PORTB pin
an input (i.e., put the corresponding output driver in a
Hi-impedance mode). Clearing a TRISB bit (=0) will
make the corresponding PORTB pin an output (i.e.,
put the contents of the output latch on the selected pin).
EXAMPLE 3-2:
Each of the PORTB pins has an internal pull-up, which
can be individually enabled from the WPUB register. A
single global enable bit can turn on/off the enabled pull-
ups. Clearing the RBPU bit, (OPTION_REG<7>),
enables the weak pull-up resistors. The 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.
BCF
CLRF
BSF
MOVLW
MOVWF
MOVLW
MOVWF
BCF
2002 Microchip Technology Inc.
PORTB and the TRISB Register
STATUS, RP0 ;
PORTB
STATUS, RP0 ; Select Bank 1
0xCF
TRISB
0x30
ANSEL
STATUS, RP0 ; Return to Bank 0
Initializing PORTB
; Initialize PORTB by
; clearing output
; data latches
; Value used to
; initialize data
; direction
; Set RB<3:0> as inputs
; RB<5:4> as outputs
; RB<7:6> as inputs
; Set RB<1:0> as analog
;
inputs
Each of the PORTB pins, if configured as input, also
has an interrupt-on-change feature, which can be indi-
vidually selected from the IOCB register. The RBIE bit
in the INTCON register functions as a global enable bit
to turn on/off the interrupt-on-change feature. The
selected inputs are compared to the old value latched
on the last read of PORTB. The "mismatch" outputs are
OR’ed together to generate the RB Port Change Inter-
rupt with flag bit RBIF (INTCON<0>).
This interrupt can wake the device from SLEEP. The
user, in the interrupt service routine, can clear the inter-
rupt in the following manner:
a)
a)
A mismatch condition will continue to set flag bit RBIF.
Reading PORTB will end the mismatch condition and
allow flag bit RBIF to be cleared.
The interrupt-on-change feature is recommended for
wake-up on key depression operation and operations
where PORTB is only used for the interrupt-on-change
feature. Polling of PORTB is not recommended while
using the interrupt-on-change feature.
PIC16C717/770/771
Any read or write of PORTB. This will end the
mismatch condition.
Clear flag bit RBIF.
DS41120B-page 33