PIC16F62X
Note 1: On reset, the TRISA register is set to all
inputs. The digital inputs are disabled and
the comparator inputs are forced to
ground to reduce excess current con-
sumption.
5.0
I/O PORTS
The PIC16F62X have two ports, PORTA and PORTB.
Some pins for these I/O ports are multiplexed with an
alternate function for the peripheral features on the
device. In general, when a peripheral is enabled, that
pin may not be used as a general purpose I/O pin.
Note 2: When RA6/OSC2/CLKOUT is configured
as CLKOUT, the corresponding TRIS bit is
overridden and the pin is configured as an
output. The PORTA data bit reads 0, and
the PORTA TRIS bit reads 0.
5.1
PORTA and TRISA Registers
PORTA is an 8-bit wide latch. RA4 is a Schmitt Trigger
input and an open drain output. Port RA4 is multiplexed
with the T0CKI clock input. RA5 is a Schmitt Trigger input
only and has no output drivers. All other RA port pins have
Schmitt Trigger input levels and full CMOS output drivers.
All pins have data direction bits (TRIS registers) which can
configure these pins as input or output.
TRISA controls the direction of the RA pins, even when
they are being used as comparator inputs. The user
must make sure to keep the pins configured as inputs
when using them as comparator inputs.
The RA2 pin will also function as the output for the
voltage reference. When in this mode, the VREF pin is a
very high impedance output. The user must configure
TRISA<2> bit as an input and use high impedance
loads.
A ’1’ in the TRISA register puts the corresponding output
driver in a hi- impedance mode. A ’0’ in the TRISA register
puts the contents of the output latch on the selected pin(s).
Reading the PORTA 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.
In one of the comparator modes defined by the
CMCON register, pins RA3 and RA4 become outputs
of the comparators. The TRISA<4:3> bits must be
cleared to enable outputs to use this function.
EXAMPLE 5-1: INITIALIZING PORTA
The PORTA pins are multiplexed with comparator and
voltage reference functions. The operation of these
pins are selected by control bits in the CMCON
(comparator control register) register and the VRCON
(voltage reference control register) register. When
selected as a comparator input, these pins will read
as ’0’s.
CLRF PORTA
;Initialize PORTA by setting
;output data latches
;Turn comparators off and
;enable pins for I/O
;functions
MOVLW 0X07
MOVWF CMCON
BCF
BSF
STATUS, RP1
STATUS, RP0 ;Select Bank1
MOVLW 0x1F
;Value used to initialize
;data direction
MOVWF TRISA
;Set RA<4:0> as inputs
;TRISA<7:5> are always
;read as ’0’.
1999 Microchip Technology Inc.
Preliminary
DS40300B-page 27
MICROCHIP [ MICROCHIP ]
