PIC18F2682 Datasheet, PDF (146/484 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with ECAN Technology, 10-Bit A/D and nanoWatt Technology

PIC18F2682/2685/4682/4685
10.6 Parallel Slave Port
Note: The Parallel Slave Port is only available on
PIC18F4682/4685 devices.
In addition to its function as a general I/O port, PORTD
can also operate as an 8-bit wide Parallel Slave Port
(PSP) or microprocessor port. PSP operation is
controlled by the 4 upper bits of the TRISE register
(Register 10-1). Setting control bit, PSPMODE
(TRISE<4>), enables PSP operation, as long as the
Enhanced CCP1 (ECCP1) module is not operating in
dual output or quad output PWM mode. In Slave mode,
the port is asynchronously readable and writable by the
external world.
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
the control bit, PSPMODE, enables the PORTE I/O
pins to become control inputs for the microprocessor
port. When set, port pin RE0 is the RD input, RE1 is the
WR input and RE2 is the CS (Chip Select) input. For
this functionality, the corresponding data direction bits
of the TRISE register (TRISE<2:0>) must be config-
ured as inputs (set). The A/D port configuration bits,
PFCG3:PFCG0 (ADCON1<3:0>), must also be set to
‘1010’.
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 are both 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 is set. If the user writes new data
to PORTD to set OBF, the data is immediately read out;
however, 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 10-3 and Figure 10-4,
respectively.
FIGURE 10-2:
PORTD AND PORTE
BLOCK DIAGRAM
(PARALLEL SLAVE PORT)
One bit of PORTD
Data Bus
D
Q
WR LATD or
WR PORTD _CK
Data Latch
TTL
Q
D
RDx pin
RD PORTD
ENEN
RD LATD
Set Interrupt Flag
PSPIF (PIR1<7>)
PORTE Pins
Read
TTL
RD
Chip
Select
TTL
CS
Write
TTL
WR
Note: I/O pins have diode protection to VDD and VSS.
DS39761B-page 144
Preliminary
© 2007 Microchip Technology Inc.