performed, during which the data is latched for the duration of the EPP write cycle. During a READ operation, PD0 -
PD7 ports are read. An LPC I/O read cycle 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 read cycle. This register
is only available in EPP mode.
EPP DATA PORT 0
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 the internal data bus DB0-DB7 are buffered (non inverting) and
output onto the PD0 - PD7 ports. An LPC I/O write cycle causes an EPP DATA WRITE cycle to be performed, during
which the data is latched for the duration of the EPP write cycle. During a READ operation, PD0 - PD7 ports are read.
An LPC I/O read cycle 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 read cycle. This register is only available in EPP
mode.
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.
EPP DATA PORT 2
ADDRESS OFFSET = 06H
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.
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 bi-
directional mode, and all output signals (STROBE, AUTOFD, INIT) are as set by the SPP Control Port and direction is
controlled by PCD of the Control port.
In EPP mode, the system timing is closely coupled to the EPP timing. For this reason, a watchdog timer is required to
prevent system lockup. The timer indicates if more than 10usec have elapsed from the start of the EPP cycle to nWAIT
being deasserted (after command). If a time-out occurs, the current EPP cycle is aborted and the time-out condition is
indicated in Status bit 0.
During an EPP cycle, if STROBE is active, it overrides the EPP write signal forcing the PDx bus to always be in a write
mode and the nWRITE signal to always be asserted.
Software Constraints
Before an EPP cycle is executed, the software must ensure that the control register bit PCD is a logic "0" (i.e., a 04H or
05H should be written to the Control port). If the user leaves PCD as a logic "1", and attempts to perform an EPP write,
the chip is unable to perform the write (because PCD is a logic "1") and will appear to perform an EPP read on the
parallel bus, no error is indicated.
EPP 1.9 Write
The timing for a write operation (address or data) is shown in timing diagram EPP Write Data or Address cycle. The
chip inserts wait states into the LPC I/O write cycle until it has been determined that the write cycle can complete. The
write cycle can complete under the following circumstances:
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