PIC18F2221 MICROCHIP [Microchip Technology], PIC18F2221 Datasheet - Page 122

• Manufacturer Part Number: PIC18F2221
• Description: 28/40/44-Pin Enhanced Flash Microcontrollers with 10-Bit A/D and nanoWatt Technology
• Manufacturer: MICROCHIP [Microchip Technology]

PIC18F4321 FAMILY
10.6
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).
(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 config-
ured 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.
DS39689E-page 120
Note:
Parallel Slave Port
The Parallel Slave Port is only available on
40/44-pin devices.
Setting
control
bit,
PSPMODE
Preliminary
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:
Note:
Data Bus
Set Interrupt Flag
PSPIF (PIR1<7>)
WR LATD
or
WR PORTD
RD LATD
RD PORTD
I/O pins have diode protection to V
Data Latch
Q
D
One bit of PORTD
CK
EN
PORTD AND PORTE
BLOCK DIAGRAM
(PARALLEL SLAVE PORT)
EN
Q
D
© 2007 Microchip Technology Inc.
Chip Select
Read
Write
DD
TTL
and V
TTL
TTL
TTL
PORTE Pins
SS
.
RDx pin
RD
CS
WR