Data Sheet High-Performance, Enhanced Flash Microcontrollers phần 4 docx

© 2006 Microchip Technology Inc. DS39564C-page 97

PIC18FXX2

9.5 PORTE, TRISE and LATE

Registers

This section is only applicable to the PIC18F4X2

devices.

PORTE is a 3-bit wide, bi-directional port. The corre￾sponding 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

Hi-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).

The Data Latch register (LATE) is also memory

mapped. Read-modify-write operations on the LATE

register reads and writes the latched output value for

PORTE.

PORTE has three pins (RE0/RD/AN5, RE1/WR/AN6

and RE2/CS/AN7) which are individually configurable

as inputs or outputs. These pins have Schmitt Trigger

input buffers.

Register 9-1 shows the TRISE register, which also

controls the parallel slave port operation.

PORTE pins are multiplexed with analog inputs. When

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

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.

EXAMPLE 9-5: INITIALIZING PORTE

FIGURE 9-9: PORTE BLOCK DIAGRAM

IN I/O PORT MODE

Note: On a Power-on Reset, these pins are

configured as analog inputs.

CLRF PORTE ; Initialize PORTE by

; clearing output

; data latches

CLRF LATE ; Alternate method

; to clear output

; data latches

MOVLW 0x07 ; Configure A/D

MOVWF ADCON1 ; for digital inputs

MOVLW 0x05 ; Value used to

; initialize data

; direction

MOVWF TRISE ; Set RE<0> as inputs

; RE<1> as outputs

; RE<2> as inputs

Data

Bus

WR LATE

WR TRISE

RD PORTE

Data Latch

TRIS Latch

RD TRISE

Schmitt

Trigger

Input

Buffer

D Q

CK

D Q

CK

EN

Q D

EN

I/O pin(1)

RD LATE

or

PORTE

To Analog Converter

Note 1: I/O pins have diode protection to VDD and VSS.

PIC18FXX2

DS39564C-page 98 © 2006 Microchip Technology Inc.

REGISTER 9-1: TRISE REGISTER

R-0 R-0 R/W-0 R/W-0 U-0 R/W-1 R/W-1 R/W-1

IBF OBF IBOV PSPMODE — TRISE2 TRISE1 TRISE0

bit 7 bit 0

bit 7 IBF: Input Buffer Full Status bit

1 = A word has been received and waiting to be read by the CPU

0 = No word has been received

bit 6 OBF: Output Buffer Full Status bit

1 = The output buffer still holds a previously written word

0 = The output buffer has been read

bit 5 IBOV: Input Buffer Overflow Detect bit (in Microprocessor mode)

1 = A write occurred when a previously input word has not been read

(must be cleared in software)

0 = No overflow occurred

bit 4 PSPMODE: Parallel Slave Port Mode Select bit

1 = Parallel Slave Port mode

0 = General purpose I/O mode

bit 3 Unimplemented: Read as '0'

bit 2 TRISE2: RE2 Direction Control bit

1 = Input

0 = Output

bit 1 TRISE1: RE1 Direction Control bit

1 = Input

0 = Output

bit 0 TRISE0: RE0 Direction Control bit

1 = Input

0 = Output

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

© 2006 Microchip Technology Inc. DS39564C-page 99

PIC18FXX2

TABLE 9-9: PORTE FUNCTIONS

TABLE 9-10: SUMMARY OF REGISTERS ASSOCIATED WITH PORTE

Name Bit# Buffer Type Function

RE0/RD/AN5 bit0 ST/TTL(1)

Input/output port pin or read control input in Parallel Slave Port mode

or analog input:

RD

1 = Not a read operation

0 = Read operation. Reads PORTD register (if chip selected).

RE1/WR/AN6 bit1 ST/TTL(1)

Input/output port pin or write control input in Parallel Slave Port mode

or analog input:

WR

1 = Not a write operation

0 = Write operation. Writes PORTD register (if chip selected).

RE2/CS/AN7 bit2 ST/TTL(1)

Input/output port pin or chip select control input in Parallel Slave Port

mode or analog input:

CS

1 = Device is not selected

0 = Device is selected

Legend: ST = Schmitt Trigger input, TTL = TTL input

Note 1: Input buffers are Schmitt Triggers when in I/O mode and TTL buffers when in Parallel Slave Port mode.

Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Value on

POR, BOR

Value on

All Other

RESETS

PORTE — — — — — RE2 RE1 RE0 ---- -000 ---- -000

LATE — — — — — LATE Data Output Register ---- -xxx ---- -uuu

TRISE IBF OBF IBOV PSPMODE — PORTE Data Direction bits 0000 -111 0000 -111

ADCON1 ADFM ADCS2 — — PCFG3 PCFG2 PCFG1 PCFG0 00-- 0000 00-- 0000

Legend: x = unknown, u = unchanged, - = unimplemented, read as '0'. Shaded cells are not used by PORTE.