SCH3112I-NE SMSC [SMSC Corporation], SCH3112I-NE Datasheet - Page 372

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

Rev 0.2 (09-28-04)
ECP PARALLEL PORT TIMING
Parallel Port FIFO (Mode 101)
The standard parallel port is run at or near the peak 500KBytes/sec allowed in the forward direction
using DMA. The state machine does not examine nACK and begins the next transfer based on Busy.
Refer to
ECP Parallel Port Timing
The timing is designed to allow operation at approximately 2.0 Mbytes/sec over a 15ft cable. If a
shorter cable is used then the bandwidth will increase.
Forward-Idle
When the host has no data to send it keeps HostClk (nStrobe) high and the peripheral will leave
PeriphClk (Busy) low.
Forward Data Transfer Phase
The interface transfers data and commands from the host to the peripheral using an interlocked
PeriphAck and HostClk. The peripheral may indicate its desire to send data to the host by asserting
nPeriphRequest.
The Forward Data Transfer Phase may be entered from the Forward-Idle Phase. While in the Forward
Phase the peripheral may asynchronously assert the nPeriphRequest (nFault) to request that the
channel be reversed. When the peripheral is not busy it sets PeriphAck (Busy) low. The host then sets
HostClk (nStrobe) low when it is prepared to send data. The data must be stable for the specified setup
time prior to the falling edge of HostClk. The peripheral then sets PeriphAck (Busy) high to
acknowledge the handshake. The host then sets HostClk (nStrobe) high. The peripheral then accepts
the data and sets PeriphAck (Busy) low, completing the transfer. This sequence is shown in
Figure 29.18 on page
The timing is designed to provide 3 cable round-trip times for data setup if Data is driven
simultaneously with HostClk (nStrobe).
Reverse-Idle Phase
The peripheral has no data to send and keeps PeriphClk high. The host is idle and keeps HostAck low.
Reverse Data Transfer Phase
The interface transfers data and commands from the peripheral to the host using an interlocked
HostAck and PeriphClk.
The Reverse Data Transfer Phase may be entered from the Reverse-Idle Phase. After the previous
byte has been accepted the host sets HostAck (nALF) low. The peripheral then sets PeriphClk (nACK)
low when it has data to send. The data must be stable for the specified setup time prior to the falling
edge of PeriphClk. When the host is ready to accept a byte it sets HostAck (nALF) high to
acknowledge the handshake. The peripheral then sets PeriphClk (nACK) high. After the host has
accepted the data, it sets HostAck (nALF) low, completing the transfer. This sequence is shown in
Figure 29.19 on page
Output Drivers
To facilitate higher performance data transfer, the use of balanced CMOS active drivers for critical
signals (Data, HostAck, HostClk, PeriphAck, PeriphClk) are used in ECP Mode. Because the use of
active drivers can present compatibility problems in Compatible Mode (the control signals, by tradition,
are specified as open-drain), the drivers are dynamically changed from open-drain to push-pull. The
timing for the dynamic driver change is specified in the IEEE 1284 Extended Capabilities Port Protocol
and ISA Interface Standard, Rev. 1.14 , July 14, 1993, available from Microsoft. The dynamic driver
change must be implemented properly to prevent glitching the outputs.
Figure 29.17 on page
358.
359.
357.
DATASHEET
LPC IO with 8042 KBC, Reset Generation, HWM and Multiple Serial Ports
356
SMSC SCH311X
Datasheet