logic "0" for an EPP write or a logic "1" for and
EPP read.
EPP 1.7 Read
The timing for a read operation (data) is shown
in timing diagram EPP 1.7 Read Data cycle.
IOCHRDY is driven active low when nWAIT is
active low during the EPP cycle. This can be
used to extend the cycle time. The read cycle
can complete when nWAIT is inactive high.
EPP 1.7 Write
The timing for a write operation (address or
data) is shown in timing diagram EPP 1.7 Write
Data or Address cycle. IOCHRDY is driven
active low when nWAIT is active low during the
EPP cycle. This can be used to extend the cycle
Read Sequence of Operation
time.
The write cycle can complete when
nWAIT is inactive high.
1. The host sets PDIR bit in the control
register to a logic "1". This deasserts
nWRITE and tri-states the PData bus.
2. The host selects an EPP register and drives
nIOR active.
Write Sequence of Operation
1. The host sets PDIR bit in the control
register to a logic "0".
nWRITE.
2. The host selects an EPP register, places
data on the SData bus and drives nIOW
active.
This asserts
3. Chip asserts nDATASTB or nADDRSTRB
indicating that PData bus is tri-stated, PDIR
is set and the nWRITE signal is valid.
4. If nWAIT is asserted, IOCHRDY is
deasserted until the peripheral deasserts
nWAIT or a time-out occurs.
5. The Peripheral drives PData bus valid.
6. The Peripheral deasserts nWAIT, indicating
that PData is valid and the chip may begin
the termination phase of the cycle.
7. When the host deasserts nIOR the chip
deasserts nDATASTB or nADDRSTRB.
8. Peripheral tri-states the PData bus.
9. Chip may modify nWRITE, PDIR and
nPDATA in preparation of the next cycle.
3. The chip places address or data on PData
bus.
4. Chip asserts nDATASTB or nADDRSTRB
indicating that PData bus contains valid
information, and the WRITE signal is valid.
5. If nWAIT is asserted, IOCHRDY is
deasserted until the peripheral deasserts
nWAIT or a time-out occurs.
6. When the host deasserts nIOW the chip
deasserts nDATASTB or nADDRSTRB and
latches the data from the SData bus for the
PData bus.
7. Chip may modify nWRITE, PDIR and
nPDATA in preparation of the next cycle.
87
SMSC [ SMSC CORPORATION ]
