
Advanced Notebook I/O for ISA or LPC Designs
Datasheet
SMSC SIO10N268
Page 129
Rev. 0.5 (03-24-05)
DATASHEET
handshake for each ECP read data byte and attempt to fill the FIFO. Bytes may then be read from the
ecpDFifo as long as it is not empty.
ECP transfers may also be accomplished (albeit slowly) by handshaking individual bytes under program
control in mode = 001, or 000.
8.10.7.3 Termination from ECP Mode
Termination from ECP Mode is similar to the termination from Nibble/Byte Modes. The host is permitted to
terminate from ECP Mode only in specific well-defined states. The termination can only be executed while
the bus is in the forward direction. To terminate while the channel is in the reverse direction, it must first be
transitioned into the forward direction.
8.10.7.4 Command/Data
ECP Mode supports two advanced features to improve the effectiveness of the protocol for some
applications. The features are implemented by allowing the transfer of normal 8 bit data or 8 bit
commands.
When in the forward direction, normal data is transferred when HostAck is high and an 8 bit command is
transferred when HostAck is low.
The most significant bit of the command indicates whether it is a run-length count (for compression) or a
channel address.
When in the reverse direction, normal data is transferred when PeriphAck is high and an 8 bit command is
transferred when PeriphAck is low. The most significant bit of the command is always zero. Reverse
channel addresses are seldom used and may not be supported in hardware.
Table 8.48 - Forward Channel Commands (HostAck Low),
Reverse Channel Commands (PeripAck Low)
D7
D[6:0]
0
Run-Length Count (0-127) (mode 0011 0X00 only)
1
Channel Address (0-127)
8.10.7.5 Data Compression
The ECP port supports run length encoded (RLE) decompression in hardware and can transfer
compressed data to a peripheral. Run length encoded (RLE) compression in hardware is not supported.
To transfer compressed data in ECP mode, the compression count is written to the ecpAFifo and the data
byte is written to the ecpDFifo.
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. When a run-length count is received from a peripheral,
the subsequent data byte is replicated the specified number of times. A run-length count of zero specifies
that only one byte of data is represented by the next data byte, whereas a run-length count of 127 indicates
that the next byte should be expanded to 128 bytes. To prevent data expansion, however, run-length
counts of zero should be avoided.