For a description of the ECP Protocol, please refer to the
IEEE 1284 Extended Capabilities Port Protocol and ISA
it provides an automatic high burst-bandwidth channel
that supports DMA for ECP in both the forward and
reverse directions.
Interface Standard, Rev. 1.09, Jan.7, 1993.
document is available from Microsoft.
This
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.
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, rather
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.
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