PIC18F4539 Datasheet, PDF (88/322 Pages) Microchip Technology – Enhanced FLASH Microcontrollers with Single Phase Induction Motor Control Kernel

PIC18FXX39
9.2 PORTB, TRISB and LATB
Registers
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
High 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).
The Data Latch register (LATB) is also memory
mapped. Read-modify-write operations on the LATB
register reads and writes the latched output value for
PORTB.
EXAMPLE 9-2: INITIALIZING PORTB
CLRF PORTB
CLRF LATB
MOVLW 0xCF
MOVWF TRISB
; Initialize PORTB by
; clearing output
; data latches
; Alternate method
; to clear 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
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 (INTCON2<7>). 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.
Note: On a Power-on Reset, these pins are
configured as digital inputs.
Four of the PORTB 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>).
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 (except with the
MOVFF instruction). 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.
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 9-4:
RBPU⁽²⁾
Data Bus
WR LATB
or PORTB
BLOCK DIAGRAM OF
RB7:RB4 PINS
VDD
Data Latch
DQ
CK
P
Weak
Pull-up
I/O pin⁽¹⁾
TRIS Latch
DQ
WR TRISB
CK
RD TRISB
TTL
Input
Buffer
ST
Buffer
RD LATB
RD PORTB
Set RBIF
Latch
QD
EN
Q1
From other
RB7:RB4 pins
QD
RD PORTB
EN
Q3
RB7:RB5 in Serial Programming mode
Note 1:
2:
I/O pins have diode protection to VDD and VSS.
To enable weak pull-ups, set the appropriate TRIS bit(s)
and clear the RBPU bit (INTCON2<7>).
Note 1: While in Low Voltage ICSP mode, the
RB5 pin can no longer be used as a gen-
eral purpose I/O pin, and should be held
low during normal operation to protect
against inadvertent ICSP mode entry.
2: When using Low Voltage ICSP program-
ming (LVP), the pull-up on RB5 becomes
disabled. If TRISB bit 5 is cleared,
thereby setting RB5 as an output, LATB
bit 5 must also be cleared for proper
operation.
DS30485A-page 86
Preliminary
 2002 Microchip Technology Inc.