EPP 1.7 Read
The timing for a read operation (data) is shown in timing diagram EPP 1.7 Read Data cycle. The chip
inserts wait states into the I/O read cycle 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 initiates an I/O read cycle to the selected EPP register.
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, the chip inserts wait states into the I/O read cycle 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. The chip drives the final sync and 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.
Table 34 - EPP Pin Descriptions
EPP
SIGNAL
EPP NAME
TYPE
nWRITE
nWrite
O
This signal is active low. It denotes a write operation.
PD<0:7>
Address/Data
I/O
Bi-directional EPP byte wide address and data bus.
INTR
Interrupt
I
This signal is active high and positive edge triggered. (Pass
through with no inversion, Same as SPP).
WAIT
nWait
I
This signal is active low. It is driven inactive as a positive
acknowledgement from the device that the transfer of data is
completed. It is driven active as an indication that the device is
ready for the next transfer.
DATASTB
nData Strobe
O
This signal is active low. It is used to denote data read or write
operation.
RESET
nReset
O
This signal is active low. When driven active, the EPP device
is reset to its initial operational mode.
ADDRSTB
nAddress
Strobe
write operation.
PE
Paper End
I
Same as SPP mode.
SLCT
Printer Selected
Status
nERR
Error
I
Same as SPP mode.
Note 1: SPP and EPP can use 1 common register.
Note 2: nWrite is the only EPP output that can be over-ridden by SPP control port during an EPP cycle.
For correct EPP read cycles, PCD is required to be a low.
Extended Capabilities Parallel Port
ECP provides a number of advantages, some of which are listed below. The individual features are
explained in greater detail in the remainder of this section.
97
EPP DESCRIPTION
O
This signal is active low. It is used to denote address read or
I
Same as SPP mode.