PIC16F877A-I/P【PDF 182/234 页】IC MCU FLASH 8KX14 EE 40DIP

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2003 Microchip Technology Inc.

DS39582B-page 49

PIC16F87XA

4.5

PORTE and TRISE Register

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.

The PORTE pins become the I/O control inputs for the

microprocessor port when bit PSPMODE (TRISE<4>) is

set. In this mode, the user must make certain that the

TRISE<2:0> bits are set and that the pins are configured

as digital inputs. Also, ensure that ADCON1 is config-

ured for digital I/O. In this mode, the input buffers are

TTL.

controls the Parallel Slave Port operation.

PORTE pins are multiplexed with analog inputs. When

selected for 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.

FIGURE 4-9:

PORTE BLOCK DIAGRAM

(IN I/O PORT MODE)

TABLE 4-9:

PORTE FUNCTIONS

Note:

PORTE and TRISE are not implemented

on the 28-pin devices.

Note:

On a Power-on Reset, these pins are

configured as analog inputs and read as ‘0’.

Data

Bus

Port

TRIS

RD Port

Data Latch

TRIS Latch

Schmitt

Trigger

Input

Buffer

I/O pin(1)

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

TRIS

Name

Bit#

Buffer Type

Function

RE0/RD/AN5

bit 0

ST/TTL(1)

I/O port pin or read control input in Parallel Slave Port mode or analog input:

=Idle

= Read operation. Contents of PORTD register are output to PORTD

I/O pins (if chip selected).

RE1/WR/AN6

bit 1

ST/TTL(1)

I/O port pin or write control input in Parallel Slave Port mode or analog input:

=Idle

= Write operation. Value of PORTD I/O pins is latched into PORTD

RE2/CS/AN7

bit 2

ST/TTL(1)

I/O port pin or chip select control input in Parallel Slave Port mode or analog input:

= Device is not selected

= 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.

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