PIC16LF1904 Datasheet, PDF (102/288 Pages) Microchip Technology – 28/40/44-Pin Flash-Based, 8-Bit CMOS Microcontrollers with LCD Driver and nanoWatt XLP Technology

PIC16LF1904/6/7
11.1 PORTA Registers
PORTA is an 8-bit wide, bidirectional port. The
corresponding data direction register is TRISA
(Register 11-2). 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). The exception is RA3, which is
input only and its TRIS bit will always read as ‘1’.
Example 11-1 shows how to initialize PORTA.
Reading the PORTA register (Register 11-1) 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 11-2) 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’.
11.1.1 ANSELA REGISTER
The ANSELA register (Register 11-4) 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.
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.
11.1.2
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, comparator and
CapSense 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.
TABLE 11-2: PORTA OUTPUT PRIORITY
Pin Name
Function Priority⁽¹⁾
RA0
SEG12 (LCD)
AN0
RA0
RA1
SEG7
AN1
RA1
RA2
COM2
AN2
RA2
RA3
VREF+
COM3
SEG15
AN3
RA3
RA4
SEG4
T0CKI
RA4
RA5
SEG5
AN4
RA5
RA6
CLKOUT
SEG1
RA6
RA7
CLKIN
SEG2
RA7
Note 1: Priority listed from highest to lowest.
DS41569A-page 102
Preliminary
 2011 Microchip Technology Inc.