PIC16C774 Microchip Technology Inc., PIC16C774 Datasheet - Page 37

• Manufacturer Part Number: PIC16C774
• Description: 28/40-pin, 8-bit Cmos Microcontrollers W/ 12-bit A/d
• Manufacturer: Microchip Technology Inc.

3.6
The Parallel Slave Port is implemented on the
40/44-pin devices only.
PORTD operates as an 8-bit wide Parallel Slave Port,
or microprocessor port when control bit PSPMODE
(TRISE<4>) is set. In slave mode it is asynchronously
readable and writable by the external world through RD
control input pin RE0/RD and WR control input pin
RE1/WR.
It can directly interface to an 8-bit microprocessor 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 configuration
bits, PCFG3:PCFG0 (ADCON1<3:0>) must be config-
ured to make pins RE2:RE0 as digital I/O.
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.
FIGURE 3-14: PARALLEL SLAVE PORT WRITE WAVEFORMS
PORTD<7:0>
1999 Microchip Technology Inc.
PSPIF
Parallel Slave Port
OBF
CS
WR
RD
IBF
Q1
Q2
Q3
Advance Information
Q4
Q1
Q2
FIGURE 3-13: PORTD AND PORTE BLOCK
One bit of PORTD
Note: I/O pin has protection diodes to V
Data bus
Set interrupt flag
PSPIF (PIR1<7>)
Q3
WR
PORT
RD
PORT
Q4
Q
D
CK
DIAGRAM (PARALLEL SLAVE
PORT)
EN
Q1
EN
Q
D
PIC16C77X
Q2
Chip Select
Read
Write
Q3
DS30275A-page 37
TTL
DD
TTL
TTL
TTL
and V
Q4
SS
CS
WR
RD
RDx
pin
.