PIC18F2X1X Datasheet, PDF (112/380 Pages) Microchip Technology – 28/40/44-PIN FLASH MICROCONTROLLERS WITH 10-BIT A/D AND NANO WATT TECHNOLOGY

PIC18F2X1X/4X1X
9.6 Parallel Slave Port
Note: The Parallel Slave Port is only available on
40/44-pin 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 con-
trolled by the 4 upper bits of the TRISE register
(Register 9-1). Setting control bit, PSPMODE
(TRISE<4>), enables PSP operation as long as the
enhanced CCP 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 configured
as inputs (set). The A/D port configuration bits,
PFCG3:PFCG0 (ADCON1<3:0>), must also be set to a
value in the range of ‘1010’ through ‘1111’.
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 clear. 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 lines are 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 9-3 and Figure 9-4,
respectively.
FIGURE 9-2:
PORTD AND PORTE
BLOCK DIAGRAM
(PARALLEL SLAVE PORT)
One bit of PORTD
Data Bus
DQ
WR LATD
or
CK
WR PORTD
Data Latch
Q
D
RDx pin
TTL
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.
DS39636A-page 110
Preliminary
 2004 Microchip Technology Inc.