rather it provides an automatic high
burst-bandwidth channel that 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 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.
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.
The port also supports run length encoded
(RLE) decompression (required) in hardware.
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.
Description
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,
90
SMSC [ SMSC CORPORATION ]
