PIC16F7X7
The other PORTA pins are multiplexed with analog
inputs, the analog VREF+ and VREF- 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.
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).
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).
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.
Reading the PORTA register reads the status of the
pins, whereas writing to it, will write to the port latch.
EXAMPLE 5-1:
INITIALIZING PORTA
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
Section 15.1 “Configuration Bits” for details). When
they are not used as port pins, RA6 and RA7 and their
associated TRIS and LAT bits are read as ‘0’.
BCF
STATUS, RP0
;
BCF
CLRF
STATUS, RP1
PORTA
; Bank0
; Initialize PORTA by
; clearing output
; data latches
; Select Bank 1
; Configure all pins
; as digital inputs
; Value used to
; initialize data
; direction
BSF
STATUS, RP0
0x0F
ADCON1
0xCF
MOVLW
MOVWF
MOVLW
MOVWF
TRISA
; Set RA<3:0> as inputs
; RA<5:4> as outputs
; TRISA<7:6>are always
; read as '0'.
2004 Microchip Technology Inc.
DS30498C-page 49
MICROCHIP [ MICROCHIP ]
