Microchip Technology AC164112 Data Sheet

PIC16F72X/PIC16LF72X

DS41341E-page 54

6.2

PORTA and the TRISA Registers

PORTA is a 8-bit wide, bidirectional port. The
corresponding data direction register is TRISA
(Register 6-3). 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). Example 6-1 shows how to
initialize PORTA.

Reading the PORTA register (Register 6-2) 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.

The TRISA register (Register 6-3) 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’.

EXAMPLE 6-1:

INITIALIZING PORTA

Note:

The ANSELA register must be initialized to
configure an analog channel as a digital
input. Pins configured as analog inputs will
read ‘0’.

BANKSEL PORTA

;

CLRF

PORTA

;Init PORTA

BANKSEL ANSELA

;

CLRF ANSELA

;digital

I/O

BANKSEL TRISA

;

MOVLW

0Ch

;Set RA<3:2> as inputs

MOVWF

TRISA

;and set RA<7:4,1:0>

;as outputs

REGISTER 6-2:

PORTA: PORTA REGISTER

R/W-x

RA7

RA6

RA5

RA4

RA3

RA2

RA1

RA0

bit 7

bit 0

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

-n = Value at POR

‘1’ = Bit is set

‘0’ = Bit is cleared

x = Bit is unknown

bit 7-0

RA<7:0>: PORTA I/O Pin bit
1

= Port pin is > V

= Port pin is < V

REGISTER 6-3:

TRISA: PORTA TRI-STATE REGISTER

R/W-1

TRISA7

TRISA6

TRISA5

TRISA4

TRISA3

TRISA2

TRISA1

TRISA0