Datasheet

PIC16C62X
DS30235J-page 28  2003 Microchip Technology Inc.
5.2 PORTB and TRISB Registers
PORTB is an 8-bit wide, bi-directional port. The
corresponding data direction register is TRISB. A '1' in
the TRISB register puts the corresponding output driver
in a High Impedance mode. A '0' in the TRISB register
puts the contents of the output latch on the selected
pin(s).
Reading PORTB register reads the status of the pins,
whereas writing to it will write to the port latch. All write
operations are read-modify-write operations. So a write
to a port implies that the port pins are first read, then
this value is modified and written to the port data latch.
Each of the PORTB pins has a weak internal pull-up
(≈200 µA typical). A single control bit can turn on all the
pull-ups. This is done by clearing the RBPU
(OPTION<7>) bit. The weak pull-up is automatically
turned off when the port pin is configured as an output.
The pull-ups are disabled on Power-on Reset.
Four of PORTB’s pins, RB<7:4>, have an interrupt on
change feature. Only pins configured as inputs can
cause this interrupt to occur (e.g., any RB<7:4> pin
configured as an output is excluded from the interrupt
on change comparison). The input pins (of RB<7:4>)
are compared with the old value latched on the last
read of PORTB. The “mismatch” outputs of RB<7:4>
are OR’ed together to generate the RBIF interrupt (flag
latched in INTCON<0>).
FIGURE 5-5: BLOCK DIAGRAM OF
RB<7:4> PINS
This interrupt can wake the device from SLEEP. The
user, in the interrupt service routine, can clear the
interrupt 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
software configurable pull-ups on these four pins allow
easy interface to a key pad and make it possible for
wake-up on key-depression. (See AN552, “Implement-
ing Wake-Up on Key Strokes.)
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 5-6: BLOCK DIAGRAM OF
RB<3:0> PINS
Data Latch
From other
RBPU
(1)
P
V
DD
I/O
QD
CK
QD
CK
QD
EN
QD
EN
Data Bus
WR PORTB
WR TRISB
Set RBIF
TRIS Latch
RD TRISB
RD PORTB
RB<7:4> pins
weak
pull-up
RD PORTB
Latch
TTL
Input
Buffer
pin
Note 1: TRISB = 1 enables weak pull-up if RBPU
= '0'
(OPTION<7>).
ST
Buffer
RB<7:6> in Serial Programming mode
Q
Q
VCC
VSS
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 inter-
rupt flag may not get set.
Data Latch
RBPU
(1)
P
V
DD
QD
CK
D
CK
QD
EN
Data Bus
WR PORTB
WR TRISB
RD TRISB
RD PORTB
weak
pull-up
RD PORTB
RB0/INT
I/O
pin
TTL
Input
Buffer
Note 1: TRISB = 1 enables weak pull-up if RBPU
= '0'
(OPTION<7>).
ST
Buffer
Q
Q
Q
VCC
VSS