Note: all FIFO data transfers are byte wide and byte aligned. Address/RLE transfers are byte-wide and only allowed in
the forward direction.
The host may switch directions by first switching to mode = 001, negotiating for the forward or reverse channel, setting
direction to 1 or 0, then setting mode = 011. When direction is 1 the hardware shall 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.
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.
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 39 − Channel Commands
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)
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.
Pin Definition
The drivers for nStrobe, nAutoFd, nInit and nSelectIn are open-collector in mode 000 and are push-pull in all other
modes.
LPC Connections
The interface can never stall causing the host to hang. The width of data transfers is strictly controlled on an I/O address
basis per this specification. All FIFO-DMA transfers are byte wide, byte aligned and end on a byte boundary. (The
PWord value can be obtained by reading Configuration Register A, cnfgA, described in the next section). Single byte
wide transfers are always possible with standard or PS/2 mode using program control of the control signals.
SMSC DS – LPC47S45x
Page 90 of 259
Rev. 07/09/2001
DATASHEET
SMSC [ SMSC CORPORATION ]
