PIC12F1822 MICROCHIP [Microchip Technology], PIC12F1822 Datasheet - Page 119

• Manufacturer Part Number: PIC12F1822
• Description: 8/14-Pin Flash Microcontrollers with nanoWatt XLP Technology
• Manufacturer: MICROCHIP [Microchip Technology]

12.2
PORTA is a 6-bit wide, bidirectional port. The
corresponding data direction register is TRISA
(Register 12-3). Setting a TRISA bit (= 1) will make the
corresponding PORTA pin an input (i.e., disable the
output driver). Clearing a TRISA bit (= 0) will make the
corresponding PORTA pin an output (i.e., enables
output driver and puts the contents of the output latch
on the selected pin). The exception is RA3, which is
input only and its TRIS bit will always read as ‘1’.
Example 12-1 shows how to initialize PORTA.
Reading the PORTA register (Register 12-2) reads the
status of the pins, whereas writing to it will write to the
PORT latch. All write operations are read-modify-write
operations. Therefore, a write to a port implies that the
port pins are read, this value is modified and then
written to the PORT data latch (LATA).
The TRISA register (Register 12-3) controls the
PORTA pin output drivers, even when they are being
used as analog inputs. The user should ensure the bits
in the TRISA register are maintained set when using
them as analog inputs. I/O pins configured as analog
input always read ‘0’.
12.2.1
The ANSELA register (Register 12-5) is used to
configure the Input mode of an I/O pin to analog.
Setting the appropriate ANSELA bit high will cause all
digital reads on the pin to be read as ‘0’ and allow
analog functions on the pin to operate correctly.
The state of the ANSELA bits has no affect on digital
output functions. A pin with TRIS clear and ANSEL set
will still operate as a digital output, but the Input mode
will be analog. This can cause unexpected behavior
when executing read-modify-write instructions on the
affected port.
EXAMPLE 12-1:
 2010 Microchip Technology Inc.
BANKSEL
CLRF
BANKSEL
CLRF
BANKSEL
CLRF
BANKSEL
MOVLW
MOVWF
Note:
PORTA Registers
ANSELA REGISTER
PORTA
PORTA
LATA
LATA
ANSELA
ANSELA
TRISA
B'00111000' ;Set RA<5:3> as inputs
TRISA
The ANSELA register must be initialized to
configure an analog channel as a digital
input. Pins configured as analog inputs will
read ‘0’.
INITIALIZING PORTA
;
;Init PORTA
;Data Latch
;
;
;digital I/O
;
;and set RA<2:0> as
;outputs
PIC12F/LF1822/16F/LF1823
Preliminary
DS41413A-page 119