PIC16F688-ISLASHML datasheet(35/204 Pages) MICROCHIP

35 / 204 page

DS41203E-page 33

PIC16F688

4.0

I/O PORTS

There are as many as twelve general purpose I/O pins

available. Depending on which peripherals are enabled,

some or all of the pins may not be available as general

purpose I/O. In general, when a peripheral is enabled,

the associated pin may not be used as a general

purpose I/O pin.

4.1

PORTA and the TRISA Registers

PORTA is a 6-bit wide, bidirectional port. The

corresponding data direction register is TRISA. 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).

The exception is RA3, which is input only and its TRISA

bit will always read as ‘1’. Example 4-1 shows how to

initialize PORTA.

Reading the PORTA register 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. RA3 reads ‘0’ when MCLRE = 1.

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 input

always read ‘0’.

EXAMPLE 4-1:

INITIALIZING PORTA

Note:

The ANSEL and CMCON0 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

MOVLW

07h

;Set RA<2:0> to

MOVWF

CMCON0

;digital I/O

BANKSEL ANSEL

;

CLRF

ANSEL

;digital I/O

MOVLW

0Ch

;Set RA<3:2> as inputs

MOVWF

TRISA

;and set RA<5:4,1:0>

;as outputs

PORTA: PORTA REGISTER

U-0

R/W-x

R/W-0

R-x

R/W-0

—

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 7-6

Unimplemented: Read as ‘0’

bit 5-0

RA<5:0>: PORTA I/O Pin bit

= Port pin is > VIH

= Port pin is < VIL

TRISA: PORTA TRI-STATE REGISTER

U-0

R/W-1

R-1

R/W-1

—

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 7-6

Unimplemented: Read as ‘0’

bit 5-0

TRISA<5:0>: PORTA Tri-State Control bits

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

= PORTA pin configured as an output

Note

TRISA<3> always reads ‘1’.

TRISA<5:4> always reads ‘1’ in XT, HS and LP Oscillator modes.

PIC16F688-I/ML 数据表(PDF) 35 Page - Microchip Technology

PIC16F688-I/ML 数据表(HTML) 35 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

数据表下载