PIC16F7X7
5.0
I/O PORTS
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.
Additional information on I/O ports may be found in the
“PICmicro
®
Mid-Range MCU Family Reference
Manual”
(DS33023).
The other PORTA pins are multiplexed with analog
inputs, the analog V
REF
+ and V
REF
- inputs and the
comparator voltage reference output. The operation of
pins RA3:RA0 and RA5 as A/D converter inputs is
selected by clearing/setting the control bits in the
ADCON1 register (A/D Control Register 1). Pins RA0
through RA5 may also be used as comparator inputs or
outputs by setting the appropriate bits in the CMCON
register.
Note:
On a Power-on Reset, RA5 and RA3:RA0
are configured as analog inputs and read
as ‘0’. RA4 is configured as a digital input.
5.1
PORTA and the TRISA Register
PORTA is a 8-bit wide, bidirectional port. The corre-
sponding data direction register is TRISA. Setting a
TRISA bit (=
1)
will make the corresponding PORTA pin
an input (i.e., put the corresponding output driver in a
high-impedance mode). Clearing a TRISA bit (=
0)
will
make the corresponding PORTA pin an output (i.e., put
the contents of the output latch on the selected pin).
Reading the PORTA register reads the status of the
pins, whereas writing to it, will write to the port latch.
The RA4 pin is multiplexed with the Timer0 module
clock input and one of the comparator outputs to
become the RA4/T0CKI/C1OUT pin. Pins RA6 and
RA7 are multiplexed with the main oscillator pins; they
are enabled as oscillator or I/O pins by the selection of
the main oscillator in Configuration Register 1H (see
for details). When
they are not used as port pins, RA6 and RA7 and their
associated TRIS and LAT bits are read as ‘0’.
The RA4/T0CKI/C1OUT pin is a Schmitt Trigger input
and an open-drain output. All other PORTA pins have
TTL input levels and full CMOS output drivers.
The TRISA register controls the direction of the RA pins
even when they are being used as analog inputs. The
user must ensure the bits in the TRISA register are
maintained set when using them as analog inputs.
EXAMPLE 5-1:
BCF
BCF
CLRF
INITIALIZING PORTA
;
;
;
;
;
;
;
;
;
;
;
;
;
;
;
Bank0
Initialize PORTA by
clearing output
data latches
Select Bank 1
Configure all pins
as digital inputs
Value used to
initialize data
direction
Set RA<3:0> as inputs
RA<5:4> as outputs
TRISA<7:6>are always
read as '0'.
STATUS, RP0
STATUS, RP1
PORTA
BSF
MOVLW
MOVWF
MOVLW
STATUS, RP0
0x0F
ADCON1
0xCF
MOVWF
TRISA
2004 Microchip Technology Inc.
DS30498C-page 49
MICROCHIP [ MICROCHIP TECHNOLOGY ]
