PIC16C62X
This interrupt can wake the device from SLEEP. The
user, in the interrupt service routine, can clear the
interrupt in the following manner:
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
theTRISB 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).
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.
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.
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 in the
Microchip Embedded Control Handbook.)
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.
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.
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 RBIF interrupt (flag
latched in INTCON<0>).
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
RB3:RB0 PINS
VDD
RBPU(2)
FIGURE 5-5: BLOCK DIAGRAM OF
weak
P
pull-up
RB7:RB4 PINS
Data Latch
Data bus
VDD
D
Q
RBPU(2)
weak
I/O
pin(1)
P
WR PortB
pull-up
Q
CK
Data Latch
Data bus
D
Q
Q
D
I/O
pin(1)
TTL
Input
Buffer
WR PortB
CK Q
WR TRISB
CK Q
TRIS Latch
D
Q
WR TRISB
TTL
Input
Buffer
Q
CK
RD TRISB
RD PortB
ST
Buffer
Q
D
EN
RD TRISB
RD PortB
Latch
D
Q
Q
RB0/INT
EN
ST
Buffer
RD Port
Set RBIF
From other
RB7:RB4 pins
D
Note 1: I/O pins have diode protection to VDD and VSS.
Note 2: TRISB = 1 enables weak pull-up if RBPU = '0'
(OPTION<7>).
EN
RD Port
RB7:RB6 in serial programming mode
Note 1: I/O pins have diode protection to VDD and VSS.
Note 2: TRISB = 1 enables weak pull-up if RBPU = '0'
(OPTION<7>).
DS30235G-page 28
Preliminary
1998 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
