PIC18F44J10-ESLASHML datasheet(96/358 Pages) MICROCHIP

96 / 358 page

PIC18F45J10 FAMILY

DS39682C-page 94

Preliminary

9.1.3

INTERFACING TO A 5V SYSTEM

Though the VDDMAX of the PIC18F45J10 family is 3.6V,

these devices are still capable of interfacing with 5V

systems, even if the VIH of the target system is above

3.6V. This is accomplished by adding a pull-up resistor

to the port pin (Figure 9-2), clearing the LAT bit for that

pin and manipulating the corresponding TRIS bit

(Figure 9-1) to either allow the line to be pulled high or

to drive the pin low. Only port pins that are tolerant of

voltages up to 5.5V can be used for this type of

interface (refer to Section 9.1.2 “Input Pins and

Voltage Considerations”).

FIGURE 9-2:

+5V SYSTEM HARDWARE

INTERFACE

EXAMPLE 9-1:

COMMUNICATING WITH

THE +5V SYSTEM

9.2

PORTA, TRISA and LATA Registers

PORTA is a 5-bit wide, bidirectional port. The corre-

sponding 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).

Reading the PORTA register reads the status of the

pins, whereas writing to it, will write to the port latch.

The Data Latch (LATA) register is also memory mapped.

Read-modify-write operations on the LATA register read

and write the latched output value for PORTA.

The other PORTA pins are multiplexed with analog

inputs, the analog VREF+ and VREF- inputs and the com-

parator voltage reference output. The operation of pins

RA3:RA0 and RA5 as A/D converter inputs is selected

by clearing or setting the control bits in the ADCON1

Pins RA0 and RA3 may also be used as comparator

inputs and RA5 may be used as the C2 comparator

output by setting the appropriate bits in the CMCON

necessary to turn off the comparators.

All PORTA pins have TTL input levels and full CMOS

output drivers.

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.

EXAMPLE 9-2:

INITIALIZING PORTA

RD7

+5V Device

PIC18F45J10

+5V

BCF

LATD, 7

; set up LAT register so

; changing TRIS bit will

; drive line low

BCF

TRISD, 7

; send a 0 to the 5V system

BCF

TRISD, 7

; send a 1 to the 5V system

Note:

On a Power-on Reset, RA5 and RA3:RA0

are configured as analog inputs and read

as ‘0’.

CLRF

PORTA

; Initialize PORTA by

; clearing output

; data latches

CLRF

LATA

; Alternate method

; to clear output

; data latches

MOVLW

07h

; Configure A/D

MOVWF

ADCON1

; for digital inputs

MOVWF

07h

; Configure comparators

MOVWF

CMCON

; for digital input

MOVLW

0CFh

; Value used to

; initialize data

; direction

MOVWF

TRISA

; Set RA<3:0> as inputs

; RA<5:4> as outputs

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