2000 Microchip Technology Inc.
DS30605C-page 31
PIC16C63A/65B/73B/74B
5.2
PORTB and TRISB Registers
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 input mode. Clearing a bit in
the TRISB register puts the contents of the output latch
on the selected pin(s).
Each of the PORTB pins has a weak internal pull-up. A
single control bit can turn on all the pull-ups. This is per-
formed by clearing bit RBPU (OPTION_REG<7>). The
weak pull-up is automatically turned off when the port
pin is configured as an output. The pull-ups are dis-
abled on a Power-on Reset.
FIGURE 5-3:
BLOCK DIAGRAM OF
RB3:RB0 PINS
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 value latched on the
last read of PORTB. The “mismatch” outputs of
RB7:RB4 are OR’d together to generate the RB Port
Change Interrupt with flag bit RBIF (INTCON<0>).
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 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, “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.
RB0/INT is an external interrupt input pin and is config-
ured using the INTEDG bit (OPTION_REG<6>).
FIGURE 5-4:
BLOCK DIAGRAM OF
RB7:RB4 PINS
Data Latch
RBPU(2)
P
VDD
Q
D
CK
Q
D
CK
QD
EN
Data Bus
WR Port
WR TRIS
RD TRIS
RD Port
Weak
Pull-up
RD Port
RB0/INT
I/O pin(1)
TTL
Input
Buffer
Schmitt Trigger
Buffer
TRIS Latch
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 RBPU bit (OPTION_REG<7>).
Data Latch
From other
RBPU(2)
P
VDD
I/O pin(1)
Q
D
CK
Q
D
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
ST
Buffer
RB7:RB6 in Serial Programming mode
Q3
Q1
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 RBPU bit (OPTION_REG<7>).
