at7601fg AME, Inc., at7601fg Datasheet - Page 20

• Manufacturer Part Number: at7601fg
• Description: Printer Port Controller
• Manufacturer: AME, Inc.

20
AT7601F
5-3-2.3 Command/Data
5-3-2.4 Data Compression
5-3-2.5 Pin Definition
5-3-2.6 ISA Connections
ECP Mode supports two advanced features to improve the effectiveness of the protocol for some applica-
tions. The features are implemented by allowing the transfer of normal 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 compres-
sion) 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.
The ECP port supports run length encoded (RLE) decompression in hardware and can transfer com-
pressed 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 ECP-AFIFO and the
data byte is written to the ECP-DFIFO.
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.
The drivers for STB#, AFD#, lNIT#
pull in all other modes.
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 Configuration Register A, Cnfg-A, de-
scribed in the next section.) single byte wide transfers are always possible with standard or PS/2 mode
using program control of the control signals.
Forward Channel Commands (HostAck Low)
Reverse Channel Commands (PeriphAck Low)
AME, Inc.
D7
0
1
Run-Length Count (0-127)
(mode 0011 0X00 only)
Channel Address (0-127)
TABLE C
D(6:0)
and SLIN# are open-collector in mode 000 and are push-
Printer Port Cotroller
Rev. B.02