PIC18F6525/6621/8525/8621
FIGURE 10-24:
PORTD AND PORTE
BLOCK DIAGRAM
(PARALLELSLAVEPORT)
10.10 Parallel Slave Port
PORTD also operates as an 8-bit wide Parallel Slave
Port, or microprocessor port, when control bit
PSPMODE (PSPCON<4>) is set. It is asynchronously
readable and writable by the external world through RD
control input pin, RE0/RD and WR control input pin,
RE1/WR.
Data Bus
D
Q
RDx
pin
WR LATD
or
PORTD
CK
Data Latch
Note:
For PIC18F8525/8621 devices, the Parallel
Slave Port is available only in
Microcontroller mode.
TTL
Q
D
The PSP can directly interface to an 8-bit micro-
processor data bus. The external microprocessor can
read or write the PORTD latch as an 8-bit latch. Setting
bit PSPMODE enables port pin RE0/RD to be the RD
input, RE1/WR to be the WR input and RE2/CS to be
the CS (chip select) input. For this functionality, the
corresponding data direction bits of the TRISE register
(TRISE<2:0>) must be configured as inputs (set). The
RD PORTD
EN
EN
TRIS Latch
RD LATD
A/D
port
configuration
bits,
PCFG2:PCFG0
One bit of PORTD
(ADCON1<2:0>), must be set, which will configure pins
RE2:RE0 as digital I/O.
Set Interrupt Flag
PSPIF (PIR1<7>)
A write to the PSP occurs when both the CS and WR
lines are first detected low. A read from the PSP occurs
when both the CS and RD lines are first detected low.
The PORTE I/O pins become control inputs for the micro-
processor port when bit PSPMODE (PSPCON<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 the ADCON1 is configured for digital I/O. In
this mode, the input buffers are TTL.
Read
RD
TTL
Chip Select
TTL
CS
Write
TTL
WR
Note: I/O pin has protection diodes to VDD and VSS.
DS39612B-page 128
2005 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
