Datasheet

 2011 Microchip Technology Inc. Preliminary DS41615A-page 101
PIC12(L)F1501
11.2 PORTA Registers
PORTA is a 6-bit wide, bidirectional port. The
corresponding data direction register is TRISA
(Register 11-3). 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 11-1 shows how to initialize an I/O port.
Reading the PORTA register (Register 11-2) 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 11-3) 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’.
11.2.1 ANSELA REGISTER
The ANSELA register (Register 11-5) 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 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.
11.2.2 PORTA FUNCTIONS AND OUTPUT
PRIORITIES
Each PORTA pin is multiplexed with other functions. The
pins, their combined functions and their output priorities
are shown in Table 11-2.
When multiple outputs are enabled, the actual pin
control goes to the peripheral with the highest priority.
Analog input functions, such as ADC and comparator
inputs, are not shown in the priority lists. These inputs
are active when the I/O pin is set for Analog mode using
the ANSELx registers. Digital output functions may
control the pin when it is in Analog mode with the
priority shown in Table 11-2.
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.
TABLE 11-2: PORTA OUTPUT PRIORITY
Pin Name Function Priority
(1)
RA0 ICSPDAT
DACOUT1
CWG1B
(2)
PWM2
RA0
RA1 NCO1
(2)
RA1
RA2 DACOUT2
CWG1A
(2)
CWG1FLT
CLC1
(2)
C1OUT
PWM1
RA2
RA3 None
RA4 CLKOUT
CWG1B
(3)
CLC1
(3)
PWM3
RA4
RA5 CWG1A
(3)
CLC2
NCO1
(3)
PWM4
RA5
Note 1: Priority listed from highest to lowest.
2: Default pin (see APFCON register).
3: Alternate pin (see APFCON register).