PIC16F913-ISLASHSS datasheet(46/330 Pages) MICROCHIP

46 / 330 page

PIC16F913/914/916/917/946

DS41250F-page 44

3.2

PORTA and TRISA Registers

PORTA is a 8-bit wide, bidirectional port. The

corresponding

data

direction

TRISA

(Register 3-3). Setting a TRISA bit (= 1) will make the

corresponding PORTA pin an input (i.e., put the

corresponding output driver in a High-Impedance mode).

Clearing a TRISA bit (= 0) will make the corresponding

PORTA pin an output (i.e., put the contents of the output

latch on the selected pin). Example 3-1 shows how to

initialize PORTA.

Five of the pins of PORTA can be configured as analog

inputs. These pins, RA5 and RA<3:0>, are configured

as analog inputs on device power-up and must be

reconfigured by the user to be used as I/O’s. This is

done by writing the appropriate values to the CMCON0

and ANSEL registers (see Example 3-1).

Reading the PORTA register (Register 3-2) 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 means that the

port pins are read, this value is modified and then written

to the PORT data latch.

The TRISA register controls the direction of the PORTA

pins, even when they are being used as analog inputs.

The user must ensure the bits in the TRISA register are

maintained set when using them as analog inputs. I/O

pins configured as analog inputs always read ‘0’.

EXAMPLE 3-1:

INITIALIZING PORTA

Note 1: The CMCON0 and ANSEL registers 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 TRISA

;

MOVLW

07h

;Set RA<2:0> to

MOVWF

CMCON0

;digital I/O

CLRF

ANSEL

;Make all PORTA digital I/O

MOVLW

0F0h

;Set RA<7:4> as inputs

MOVWF

TRISA

;and set RA<3:0> as outputs

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 bits

= Port pin is >VIH min.

= Port pin is <VIL max.

TRISA: PORTA TRI-STATE REGISTER

R/W-1

TRISA7

TRISA6

TRISA5

TRISA4

TRISA3

TRISA2

TRISA1

TRISA0

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

TRISA<7:0>: PORTA Tri-State Control bits

= PORTA pin configured as an input (tri-stated)

= PORTA pin configured as an output

Note 1:

TRISA<7:6> always reads ‘1’ in XT, HS and LP Oscillator modes.

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