SCH3112I-NE SMSC [SMSC Corporation], SCH3112I-NE Datasheet - Page 133

• Manufacturer Part Number: SCH3112I-NE
• Description: LPC IO with 8042 KBC, Reset Generation, HWM and Multiple Serial Ports
• Manufacturer: SMSC [SMSC Corporation]

LPC IO with 8042 KBC, Reset Generation, HWM and Multiple Serial Ports
Datasheet
SMSC SCH311X
Forward Channel Commands (HostAck Low)
Reverse Channel Commands (PeripAck Low)
D7
0
1
ECP OPERATION
Prior to ECP operation the Host must negotiate on the parallel port to determine if the peripheral
supports
control in mode 000.
After negotiation, it is necessary to initialize some of the port bits. The following are required:
Set Direction = 0, enabling the drivers.
Set strobe = 0, causing the nStrobe signal to default to the deasserted state.
Set autoFd = 0, causing the nAutoFd signal to default to the deasserted state.
Set mode = 011 (ECP Mode)
ECP address/RLE bytes or data bytes may be sent automatically by writing the ecpAFifo or ecpDFifo
respectively.
Note that 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 9.9 Channel/Data Commands Supported in ECP Mode
the ECP protocol. This is a somewhat complex negotiation carried out under program
Run-Length Count (0-127)
DATASHEET
117
Channel Address (0-127)
D[6:0]
(mode 0011 0X00 only)
Rev 0.2 (09-28-04)