MOTOROLA
MC68322 USER’S MANUAL
9-1
SECTION 9
PARALLEL PORT INTERFACE
The MC68322 contains a direct-connect, fully IEEE 1284 Level 2 compliant, bidirectional
parallel port interface (PPI). The PPI supports four IEEE 1284 communications modes—
compatibility (Centronics), nibble, byte, and enhanced capabilities port (ECP). It also
supports all variants of these modes, including device ID requests and run-length encoded
(RLE) data compression.
The PPI contains specific hardware to support automatic handshaking during host to
peripheral (forward) data transfers in compatibility and ECP modes, and run-length
detection and decompression of host to peripheral data during ECP transfers. This can
substantially improve data rates when operating the parallel port in compatibility or ECP
mode. When hardware handshaking is used in combination with the PPI’s dedicated DMA
controller, data rates as high as 2M per second can be achieved in ECP forward mode. The
software can disable and enable hardware handshaking to allow direct control of PPI signals
as well as to support future protocols. The remainder of IEEE 1284 operations (negotiation,
reverse data transfers, and termination cycles) must be carried out by the software. Please
note that IEEE 1284 EPP communications mode is not supported.
The PPI contains an interface controller that consists of a data receive and transmit latch,
run-length encoding decompression logic, input conditioning logic, and edge detector logic.
The RLE decompression is accomplished through a smart state machine and additional
control logic. The PPI has input conditioning logic to filter the incoming control signals.
Figure 9-1 illustrates the PPI controller block diagram.
Figure 9-1. Parallel Port Interface Controller Block Diagram
PD7–PD0
DIGITAL
FILTER/
EDGE
DETECTION
BUSY
ACK
PARALLEL PORT
DATA BUS
STATE
MACHINE
CONTROL
REGISTERS
CONTROL
REGISTERS
DATA
RECEIVE
LATCH
RLE
DECOMPRESSION
LOGIC
DATA
TRANSMIT
LATCH
SELECTIN
STROBE
AUTOFD
INIT
FAULT
SELECT
PERROR
F
re
e
sc
a
le
S
e
m
ic
o
n
d
u
c
to
r,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
c
..
.