The bit map of the Extended Parallel Port registers is:
D7
PD7
D6
D5
D4
D3
D2
D1
D0
Note
data
PD6
PD5
PD4
PD3
PD2
PD1
PD0
ecpAFifo
dsr
Addr/RLE
nBusy
0
Address or RLE field
2
1
1
2
2
2
nAck
0
PError
Select
ackIntEn
nFault
0
0
0
dcr
Direction
SelectIn
nInit
autofd
strobe
cFifo
ecpDFifo
tFifo
Parallel Port Data FIFO
ECP Data FIFO
Test FIFO
cnfgA
cnfgB
ecr
0
0
0
1
0
0
0
0
compress
intrValue
MODE
Parallel Port IRQ
nErrIntrEn
Parallel Port DMA
dmaEn
serviceIntr
full
empty
Note 1: These registers are available in all modes.
Note 2: All FIFOs use one common 16 byte FIFO.
Note 3: The ECP Parallel Port Config Reg B reflects the IRQ and DRQ selected by the Configuration
Registers.
supports DMA for ECP in both the forward and
reverse directions.
ISA IMPLEMENTATION STANDARD
This specification describes the standard ISA
interface to the Extended Capabilities Port (ECP).
All ISA devices supporting ECP must meet the
requirements contained in this section or the port
Small FIFOs are employed in both forward and
reverse directions to smooth data flow and
improve the maximum bandwidth requirement.
The size of the FIFO is 16 bytes deep. The port
supports an automatic handshake for the standard
parallel port to improve compatibility mode transfer
speed.
will not be supported by Microsoft. For
a
description of the ECP Protocol, please refer to the
IEEE 1284 Extended Capabilities Port Protocol
and ISA Interface Standard, Rev. 1.14, July 14,
1993. This document is available from Microsoft.
The port also supports run length encoded (RLE)
decompression
(required)
in
hardware.
Description
Compression is accomplished by counting
identical bytes and transmitting an RLE byte that
indicates how many times the next byte is to be
repeated. Decompression simply intercepts the
RLE byte and repeats the following byte the
specified number of times. Hardware support for
compression is optional.
The port is software and hardware compatible with
existing parallel ports so that it may be used as a
standard LPT port if ECP is not required. The port
is designed to be simple and requires a small
number of gates to implement. It does not do any
"protocol" negotiation, rather it provides an
automatic high burst-bandwidth channel that
97
SMSC [ SMSC CORPORATION ]
