Microchip Technology AC244044 Data Sheet
2010-2012 Microchip Technology Inc.
DS41440C-page 123
PIC16(L)F1825/1829
12.2
PORTA Registers
). 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’.
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’.
shows how to initialize a port.
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. 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 (
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 (
) 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’.
The INLVLA register (
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’.
The INLVLA register (
) controls the input
voltage threshold for each of the available PORTA input
pins. A selection between the Schmitt Trigger CMOS or
the TTL Compatible thresholds is available. The input
threshold is important in determining the value of a
read of the PORTA register and also the level at which
an Interrupt-on-Change occurs, if that feature is
enabled. See
pins. A selection between the Schmitt Trigger CMOS or
the TTL Compatible thresholds is available. The input
threshold is important in determining the value of a
read of the PORTA register and also the level at which
an Interrupt-on-Change occurs, if that feature is
enabled. See
for more information on
threshold levels.
12.2.1
ANSELA REGISTER
The ANSELA register (
) 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 effect 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.
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 effect 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 12-2:
INITIALIZING PORTA
Note:
Changing the input threshold selection
should be performed while all peripheral
modules are disabled. Changing the
threshold level during the time a module is
active may inadvertently generate a
transition associated with an input pin,
regardless of the actual voltage level on
that pin.
should be performed while all peripheral
modules are disabled. Changing the
threshold level during the time a module is
active may inadvertently generate a
transition associated with an input pin,
regardless of the actual voltage level on
that pin.
Note:
The ANSELA bits default to the Analog
mode after Reset. To use any pins as
digital general purpose or peripheral
inputs, the corresponding ANSEL bits
must be initialized to ‘0’ by user software.
mode after Reset. To use any pins as
digital general purpose or peripheral
inputs, the corresponding ANSEL bits
must be initialized to ‘0’ by user software.
BANKSEL PORTA
;
CLRF
PORTA
;Init PORTA
BANKSEL LATA
;Data Latch
CLRF
LATA
;
BANKSEL ANSELA
;
CLRF ANSELA
;digital
I/O
BANKSEL TRISA
;
MOVLW
B'00111000' ;Set RA<5:3> as inputs
MOVWF
TRISA
;and set RA<2:0> as
;outputs
;outputs