5. Chip asserts nDATASTB or nADDRSTRB
indicating that PData bus contains valid
information, and the WRITE signal is valid.
6. Peripheral deasserts nWAIT, indicating that
any setup requirements have been satisfied
and the chip may begin the termination
phase of the cycle.
7. a) The chip deasserts nDATASTB or
nADDRSTRB, this marks the beginning
of the termination phase. If it has not
already done so, the peripheral should
latch the information byte now.
Software Constraints
Before an EPP cycle is executed, the software
must ensure that the control register bit PCD is
a logic "0" (ie 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.
b) The chip latches the data from the
SData bus for the PData bus and
asserts (releases) IOCHRDY allowing
the host to complete the write cycle.
EPP 1.9 Write
The timing for a write operation (address or
data) is shown in timing diagram EPP Write
Data or Address cycle. IOCHRDY is driven
active low at the start of each EPP write and is
released when it has been determined that the
write cycle can complete. The write cycle can
complete under the following circumstances:
8. Peripheral asserts nWAIT, indicating to the
host that any hold time requirements have
been satisfied and acknowledging the
termination of the cycle.
9. Chip may modify nWRITE and nPDATA in
preparation for the next cycle.
1. If the EPP bus is not ready (nWAIT is active
low) when nDATASTB or nADDRSTB goes
active then the write can complete when
nWAIT goes inactive high.
EPP 1.9 Read
The timing for a read operation (data) is shown
in timing diagram EPP Read Data cycle.
IOCHRDY is driven active low at the start of
each EPP read and is released when it has been
determined that the read cycle can complete.
The read cycle can complete under the following
circumstances:
2. If the EPP bus is ready (nWAIT is inactive
high) then the chip must wait for it to go
active low before changing the state of
nDATASTB, nWRITE or nADDRSTB. The
write can complete once nWAIT is
determined inactive.
1
If the EPP bus is not ready (nWAIT is active
low) when nDATASTB goes active then the
read can complete when nWAIT goes
inactive high.
Write Sequence of operation
1. The host selects an EPP register, places
data on the SData bus and drives nIOW
active.
2. The chip drives IOCHRDY inactive (low).
3. If WAIT is not asserted, the chip must wait
until WAIT is asserted.
2. If the EPP bus is ready (nWAIT is inactive
high) then the chip must wait for it to go
active low before changing the state of
WRITE or before nDATASTB goes active.
The read can complete once nWAIT is
determined inactive.
4. The chip places address or data on PData
bus, clears PDIR, and asserts nWRITE.
86
SMSC [ SMSC CORPORATION ]
