PIC16F87X datasheet(36/200 Pages) MICROCHIP

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PIC16F87X

DS30292A-page 36

Preliminary

3.5

PORTE and TRISE Register

This section is not applicable to the 28-pin devices.

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.

I/O PORTE becomes control inputs for the micropro-

cessor port when bit PSPMODE (TRISE<4>) is set. In

this mode, the user must make sure that the

TRISE<2:0> bits are set (pins are conﬁgured as digital

inputs). Ensure ADCON1 is conﬁgured for digital I/O. In

this mode the input buffers are TTL.

Figure 3-9 shows the TRISE register, which also con-

trols 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.

FIGURE 3-8:

PORTE BLOCK DIAGRAM (IN

I/O PORT MODE)

FIGURE 3-9:

TRISE REGISTER (ADDRESS 89h)

Note:

On a Power-on Reset these pins are con-

ﬁgured as analog inputs.

Data

bus

PORT

TRIS

RD PORT

Data Latch

TRIS Latch

RD TRIS

Schmitt

Trigger

input

buffer

I/O pin(1)

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

R-0

R/W-0

U-0

R/W-1

IBF

OBF

IBOV

PSPMODE —

bit2

bit1

bit0

R= Readable bit

W= Writable bit

U= Unimplemented bit,

read as ‘0’

- n= Value at POR reset

bit7

bit0

bit 7 :

IBF: Input Buffer Full Status bit

1 = A word has been received and is 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'

PORTE Data Direction Bits

bit 2:

Bit2: Direction Control bit for pin RE2/CS/AN7

1 = Input

0 = Output

bit 1:

Bit1: Direction Control bit for pin RE1/WR/AN6

1 = Input

0 = Output

bit 0:

Bit0: Direction Control bit for pin RE0/RD/AN5

1 = Input

0 = Output

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