
SMSC DS – FDC37N958FR
Page 108
Rev. 09/01/99
Software Constraints
Before an EPP cycle is executed, the software
must ensure that the control register bits D0, D1
and D3 are set to zero. Also, bit D5 (PCD) is a
logic "0" for an EPP write or a logic "1" for and
EPP read.
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 time. The
write cycle can complete when nWAIT is inactive
high.
Write Sequence of Operation
1. The host sets PDIR bit in the control register
to a logic "0". This asserts nWRITE.
2. The host selects an EPP register, places data
on the SData bus and drives nIOW active.
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,
deasserted until the peripheral deasserts
nWAIT or a time-out occurs.
6. When the host deasserts nIOW the chip
deasserts nDATASTB or nADDRSTRB and
IOCHRDY
is
latches the data from the SData bus for the
PData bus.
Chip may modify nWRITE, PDIR and
nPDATA in preparation of the next cycle.
7.
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.
Read Sequence of Operation
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.
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,
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 reparation of the next cycle.
IOCHRDY
is