PIC16F913 datasheet(33/272 Pages) MICROCHIP

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Preliminary

DS41250E-page 31

PIC16F917/916/914/913

3.0

I/O PORTS

This device includes four 8-bit port registers along with

their corresponding TRIS registers and one four bit

port:

• PORTA and TRISA

• PORTB and TRISB

• PORTC and TRISC

• PORTD and TRISD

• PORTE and TRISE

PORTA, PORTB, PORTC and RE3/MCLR/VPP are

implemented on all devices. PORTD and RE<2:0> are

implemented only on the PIC16F914 and PIC16F917.

3.1

PORTA and TRISA Registers

PORTA

8-bit

wide,

bidirectional

port.

The

corresponding

data

direction

TRISA

(Register 3-2). 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 3-1) 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.

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

inputs. I/O pins configured as analog input always read

‘0’.

EXAMPLE 3-1:

INITIALIZING PORTA

Note 1: The CMCON0 (9Ch) register must be

initialized to configure an analog channel

as a digital input. Pins configured as

analog inputs will read ‘0’.

2: Analog lines that carry LCD signals

(i.e., SEGx, COMy, where x and y are

segment and common identifiers) are

shown as direct connections to the device

pins. The signals are outputs from the

LCD module and may be tri-stated,

depending on the configuration of the

LCD module.

BCF

STATUS,RP0

;Bank 0

BCF

STATUS,RP1

;

CLRF

PORTA

;Init PORTA

BSF

STATUS,RP0

;Bank 1

BCF

STATUS,RP1

;

MOVLW

07h

;Set RA<2:0> to

MOVWF

CMCON0

;digital I/O

CLF

ANSEL

;Make all PORTA I/O

MOVLW

F0h

;Set RA<7:4> as inputs

MOVWF

TRISA

;and set RA<3:0>

; as outputs

BCF

STATUS,RP0

;Bank 0

BCF

STATUS,RP1

;

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