Rev. 3.0, 03/01, page 174 of 390
(5) EPP Data Port 0 - 3
The EPP Data Port 0 - 3 are only available in EPP mode. When the host writes to these ports, the
contents of D0 - D7 are buffered and output to PD0 - PD7 as an EPP DATA Write cycle. When the
host reads from these ports, the contents of PD0 - PD7 are buffered and output to D0-D7, and
causes an EPP DATA Read Cycle.
13.3.2
ECP Mode
This mode is both software and hardware compatible with that of the existing parallel ports,
allowing ECP to be used as a standard LPT port when ECP is not required. It provides an
automatic high-burst-bandwidth channel that supports ECP in both forward and reverse directions.
A 16-byte FIFO is implemented in both forward and reverse directions to smooth data flow and
improve the maximum bandwidth requirement. The port supports an automatic handshaking for the
standard parallel port to improve compatibility and increase the speed of mode transfer. It also
supports run-length encoded (RLE) decompression in hardware. Compression is accomplished by
counting identical bytes and transmitting an RLE byte that indicates how many times a byte is
repeated.
Table 13.5
Bit Map of the ECP Mode Register
Register
D7
D6
D5
D4
D3
D2
D1
D0
data
PD7
PD6
PD5
PD4
PD3
PD2
PD1
PD0
ecpAFifo
Addr/RLE Address or RLE field
dsr
nBusy
nAck
PError
Select
nFault
1
1
1
dcr
1
1
PDDIR
IRQE
SelectIn
nInit
AutoFd
Strobe
cFifo
Parallel Port Data FIFO
ecpDFifo
ECP Data FIFO
tFifo
Test FIFO
cnfgA
0
0
0
1
0
0
0
0
cnfgB
0
intrValue 0
0
0
0
0
0
ecr
mode
nErrIntrEn
ServiceIntr full
empty
Содержание HD64465
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