PIC16F737-I/SP【PDF 6/231 页】IC PIC MCU FLASH 4KX14 28DIP

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2009 Microchip Technology Inc.

DS39636D-page 109

PIC18F2X1X/4X1X

9.5

PORTE, TRISE and LATE

Registers

Depending on the particular PIC18F2X1X/4X1X device

selected, PORTE is implemented in two different ways.

For 40/44-pin devices, PORTE is a 4-bit wide port.

Three pins (RE0/RD/AN5, RE1/WR/AN6 and RE2/CS/

AN7) are individually configurable as inputs or outputs.

These pins have Schmitt Trigger input buffers. When

selected as an analog input, these pins will read as ‘0’s.

The corresponding data direction register is TRISE.

Setting a TRISE bit (= 1) will make the corresponding

PORTE pin an input (i.e., put the corresponding output

driver in a high-impedance mode). Clearing a TRISE bit

(= 0) will make the corresponding PORTE pin an output

(i.e., put the contents of the output latch on the selected

pin).

TRISE controls the direction of the RE pins, even when

they are being used as analog inputs. The user must

make sure to keep the pins configured as inputs when

using them as analog inputs.

The upper four bits of the TRISE register also control

the operation of the Parallel Slave Port. Their operation

is explained in Register 9-1.

The Data Latch register (LATE) is also memory

mapped. Read-modify-write operations on the LATE

PORTE.

The fourth pin of PORTE (MCLR/VPP/RE3) is an input

only pin. Its operation is controlled by the MCLRE Con-

figuration bit. When selected as a port pin (MCLRE = 0),

it functions as a digital input only pin; as such, it does not

have TRIS or LAT bits associated with its operation.

Otherwise, it functions as the device’s Master Clear

input. In either configuration, RE3 also functions as the

programming voltage input during programming.

EXAMPLE 9-5:

INITIALIZING PORTE

9.5.1

PORTE IN 28-PIN DEVICES

For 28-pin devices, PORTE is only available when

Master Clear functionality is disabled (MCLRE = 0). In

these cases, PORTE is a single bit, input only port

comprised of RE3 only. The pin operates as previously

described.

Note:

On a Power-on Reset, RE2:RE0 are

configured as analog inputs.

Note:

On a Power-on Reset, RE3 is enabled as

a digital input only if Master Clear

functionality is disabled.

CLRF

PORTE

; Initialize PORTE by

; clearing output

; data latches

CLRF

LATE

; Alternate method

; to clear output

; data latches

MOVLW

0Ah

; Configure A/D

MOVWF

ADCON1 ; for digital inputs

MOVLW

03h

; Value used to

; initialize data

; direction

MOVWF

TRISE

; Set RE<0> as inputs

; RE<1> as outputs

; RE<2> as inputs

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