Datasheet

 1997-2013 Microchip Technology Inc. DS30234E-page 53
PIC16C6X
5.2 PORTB and TRISB Register
PORTB is an 8-bit wide bi-directional port. The corre-
sponding data direction register is TRISB. Setting a bit
in the TRISB register puts the corresponding output
driver in a hi-impedance mode. Clearing a bit in the
TRISB register puts the contents of the output latch on
the selected pin(s).
EXAMPLE 5-2: INITIALIZING PORTB
BCF STATUS, RP0 ;
CLRF PORTB ; Initialize PORTB by
; clearing output
; data latches
BSF STATUS, RP0 ; Select Bank 1
MOVLW 0xCF ; Value used to
; initialize data
; direction
MOVWF TRISB ; Set RB<3:0> as inputs
; RB<5:4> as outputs
; RB<7:6> as inputs
Each of the PORTB pins has a weak internal pull-up. A
single control bit can turn on all the pull-ups. This is
performed by clearing bit R
BPU (OPTION<7>). The
weak pull-up is automatically turned off when the port
pin is configured as an output. The pull-ups are also
disabled on a Power-on Reset.
Four of PORTB’s pins, RB7:RB4, have an interrupt on
change feature. Only pins configured as inputs can
cause this interrupt to occur (i.e., any RB7:RB4 pin
configured as an output is excluded from the interrupt
on change comparison). The input pins (of RB7:RB4)
are compared with the old value latched on the last
read of PORTB. The “mismatch” outputs of RB7:RB4
are OR’ed together to generate the RB port change
interrupt with flag bit RBIF (INTCON<0>).
Applicable Devices
61 62 62A R62 63 R63 64 64A R64 65 65A R65 66 67
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) Any read or write of PORTB. This will end the
mismatch condition.
b) Clear flag bit RBIF.
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.
This interrupt on mismatch feature, together with soft-
ware configurable pull-ups on these four pins allow
easy interface to a keypad and make it possible for
wake-up on key-depression. Refer to the Embedded
Control Handbook, Application Note,
“Implementing
Wake-up on Key Stroke” (AN552)
.
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.
FIGURE 5-3: BLOCK DIAGRAM OF THE
RB7:RB4 PINS FOR
PIC16C61/62/64/65
Note: For PIC16C61/62/64/65, if a change on the
I/O pin should occur when a read operation
is being executed (start of the Q2 cycle),
then interrupt flag bit RBIF may not get set.
Data Latch
From other
RBPU
(2)
P
V
DD
I/O
QD
CK
QD
CK
QD
EN
QD
EN
Data bus
WR Port
WR TRIS
Set RBIF
TRIS Latch
RD TRIS
RD Port
RB7:RB4 pins
weak
pull-up
RD Port
Latch
TTL
Input
Buffer
pin
(1)
Note 1: I/O pins have diode protection to VDD and VSS.
2: To enable weak pull-ups, set the appropriate TRIS bit(s)
and clear the RPBU
bit (OPTION<7>).
ST
Buffer
RB7:RB6 in serial programming mode