BIT 2 nINIT - nINITIATE OUTPUT
This bit is output onto the nINIT output without
inversion.
ADDRESS OFFSET = 04H
The EPP Data Port 0 is located at an offset of
'04H' from the base address. The data register is
cleared at initialization by RESET. During a
WRITE operation, the contents of DB0-DB7 are
buffered (non inverting) and output onto the PD0 -
PD7 ports, the leading edge of nIOW causes an
EPP DATA WRITE cycle to be performed, the
trailing edge of IOW latches the data for the
duration of the EPP write cycle. During a READ
operation, PD0 - PD7 ports are read, the leading
edge of IOR causes an EPP READ cycle to be
performed and the data output to the host CPU,
the deassertion of DATASTB latches the PData
for the duration of the IOR cycle. This register is
only available in EPP mode.
BIT 3 SLCTIN - PRINTER SELECT INPUT
This bit is inverted and output onto the nSLCTIN
output. A logic 1 on this bit selects the printer; a
logic 0 means the printer is not selected.
BIT 4 IRQE - INTERRUPT REQUEST ENABLE
The interrupt request enable bit when set to a high
level may be used to enable interrupt requests
from the Parallel Port to the CPU. An interrupt
request is generated on the IRQ port by a positive
going nACK input.
When the IRQE bit is
programmed low the IRQ is disabled.
BIT 5 PCD - PARALLEL CONTROL DIRECTION
Parallel Control Direction is not valid in printer
mode. In printer mode, the direction is always out
regardless of the state of this bit. In bi-directional,
EPP or ECP mode, a logic 0 means that the
printer port is in output mode (write); a logic 1
means that the printer port is in input mode (read).
EPP DATA PORT 1
ADDRESS OFFSET = 05H
The EPP Data Port 1 is located at an offset of
'05H' from the base address. Refer to EPP DATA
PORT 0 for a description of operation. This
register is only available in EPP mode.
Bits 6 and 7 during a read are a low level, and
cannot be written.
EPP DATA PORT 2
ADDRESS OFFSET = 06H
EPP ADDRESS PORT
ADDRESS OFFSET = 03H
The EPP Data Port 2 is located at an offset of
'06H' from the base address. Refer to EPP DATA
PORT 0 for a description of operation. This
register is only available in EPP mode.
The EPP Address Port is located at an offset of
'03H' from the base address. The address
register is cleared at initialization by RESET.
During a WRITE operation, the contents of DB0-
DB7 are buffered (non inverting) and output onto
the PD0 - PD7 ports, the leading edge of nIOW
causes an EPP ADDRESS WRITE cycle to be
performed, the trailing edge of IOW latches the
data for the duration of the EPP write cycle.
During a READ operation, PD0 - PD7 ports are
read, the leading edge of IOR causes an EPP
ADDRESS READ cycle to be performed and the
data output to the host CPU, the deassertion of
ADDRSTB latches the PData for the duration of
the IOR cycle. This register is only available in
EPP mode.
EPP DATA PORT 3
ADDRESS OFFSET = 07H
The EPP Data Port 3 is located at an offset of
'07H' from the base address. Refer to EPP DATA
PORT 0 for a description of operation. This
register is only available in EPP mode.
EPP 1.9 OPERATION
When the EPP mode is selected in the
configuration register, the standard and bi-
directional modes are also available. If no EPP
Read, Write or Address cycle is currently
executing, then the PDx bus is in the standard or
EPP DATA PORT 0
89
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