Datasheet

PIC10(L)F320/322
DS41585A-page 76 Preliminary  2011 Microchip Technology Inc.
10.1 PORTA Registers
PORTA is a 8-bit wide, bidirectional port. The
corresponding data direction register is TRISA
(Register 10-2). 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). Example 10-1 shows how to
initialize PORTA.
Reading the PORTA register (Register 10-1) 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 10-2) 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’.
10.1.1 WEAK PULL-UPS
Each of the PORTA pins has an individually configu-
rable internal weak pull-up. Control bits WPUA<3:0>
enable or disable each pull-up (see Register 10-5).
Each weak pull-up is automatically turned off when the
port pin is configured as an output. All pull-ups are dis-
abled on a Power-on Reset by the WPUEN
bit of the
OPTION_REG register.
10.1.2 ANSELA REGISTER
The ANSELA register (Register 10-4) 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.
10.1.3 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 10-1.
When multiple outputs are enabled, the actual pin
control goes to the peripheral with the highest priority.
Digital output functions may control the pin when it is in
Analog mode with the priority shown in Table 10-1.
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 10-1: PORTA OUTPUT PRIORITY
Pin Name Function Priority
(1)
RA0 ICSPDAT
CWG1A
PWM1
RA0
RA1 CWG1B
PWM2
CLC1
RA1
RA2 NCO1
CLKR
RA2
RA3 None
Note 1: Priority listed from highest to lowest.