Datasheet

 1997 Microchip Technology Inc. DS30390E-page 51
PIC16C7X
5.5 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.
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) and that register ADCON1 is configured for dig-
ital I/O. In this mode the input buffers are TTL.
Figure 5-9 shows the TRISE register, which also con-
trols the parallel slave port operation.
PORTE pins are multiplexed with analog inputs. The
operation of these pins is selected by control bits in the
ADCON1 register. 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.
Applicable Devices
72 73 73A 74 74A 76 77
FIGURE 5-8: PORTE BLOCK DIAGRAM (IN
I/O PORT MODE)
Note: On a Power-on Reset these pins are con-
figured as analog inputs.
Data
bus
WR
PORT
WR
TRIS
RD PORT
Data Latch
TRIS Latch
RD TRIS
Schmitt
Trigger
input
buffer
QD
CK
QD
CK
EN
QD
EN
I/O pin
(1)
Note 1: I/O pins have protection diodes to VDD and VSS.
FIGURE 5-9: TRISE REGISTER (ADDRESS 89h)
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 — 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