PIC18F87K22 Datasheet, PDF (187/548 Pages) Microchip Technology – 64/80-Pin, High-Performance, 1-Mbit Enhanced Flash Microcontrollers with 12-Bit A/D and nanoWatt XLP Technology

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12.11 Parallel Slave Port
PORTD can function as an 8-bit-wide Parallel Slave
Port (PSP), or microprocessor port, when control bit,
PSPMODE (PSPCON<4>), is set. The port is asyn-
chronously readable and writable by the external world
through the RD control input pin (RE0/P2D/RD/AD8)
and WR control input pin (RE1/P2C/WR/AD9).
Note: The Parallel Slave Port is available only in
Microcontroller mode.
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 eight-bit latch.
Setting bit, PSPMODE, enables port pin,
RE0/P2D/RD/AD8, to be the RD input,
RE1/P2C/WR/AD9 to be the WR input and
RE2/P2B/CCP10/CS/AD10 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 (= 111).
A write to the PSP occurs when both the CS and WR
lines are first detected low and ends when either are
detected high. The PSPIF and IBF flag bits (PIR1<7>
and PSPCON<7>, respectively) are set when the write
ends.
A read from the PSP occurs when both the CS and RD
lines are first detected low. The data in PORTD is read
out and the OBF bit (PSPCON<6>) is set. If the user
writes new data to PORTD to set OBF, the data is
immediately read out, but the OBF bit is not set.
When either the CS or RD line is detected high, the
PORTD pins return to the input state and the PSPIF bit
is set. User applications should wait for PSPIF to be set
before servicing the PSP. When this happens, the IBF
and OBF bits can be polled and the appropriate action
taken.
The timing for the control signals in Write and Read
modes is shown in Figure 12-4 and Figure 12-5,
respectively.
FIGURE 12-3:
PORTD AND PORTE
BLOCK DIAGRAM
(PARALLEL SLAVE PORT)
Data Bus
D
Q
WR LATD
or
PORTD
CK
Data Latch
Q
D
RD PORTD
ENEN
TRIS Latch
RDx
Pin
TTL
RD LATD
One Bit of PORTD
Set Interrupt Flag
PSPIF (PIR1<7>)
Read
TTL
RD
Chip Select
TTL
CS
Write
TTL
WR
Note: The I/O pin has protection diodes to VDD and VSS.
 2010 Microchip Technology Inc.
Preliminary
DS39960B-page 187