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W83627UHG
Publication Release Date: March 24, 2008
-118-
Revision 1.44
11.2.6
EPP Pin Descriptions
EPP NAME
TYPE
EPP DESCRIPTION
NWrite
O
Denotes read or write operation for address or data.
PD<7:0>
I/O
Bi-directional EPP address and data bus.
Intr
I
Used by peripheral devices to interrupt the host.
NWait
I
Inactivated to acknowledge that data transfer is complete. Activated to
indicate that the device is ready for the next transfer.
PE
I
Paper end; same as SPP mode.
Select
I
Printer-select status; same as SPP mode.
NDStrb
O
This signal is active low. It denotes a data read or write operation.
Nerror
I
Error; same as SPP mode.
Ninits
O
This signal is active low. When it is active, the EPP device is reset to its
initial operating mode.
NAStrb
O
This signal is active low. It denotes an address read or write operation.
11.2.7
EPP Operation
When EPP mode is selected, the PDx bus is in standard or bi-directional mode when no EPP read,
write, or address cycle is being executed. In this situation, all output signals are set by the SPP
Control Port and the direction is controlled by DIR of the Control Port.
A watchdog timer is required to prevent system lockup. The timer indicates that more than 10
μS have
elapsed from the start of the EPP cycle to the time WAIT# is deasserted. The current EPP cycle is
aborted when a time-out occurs. The time-out condition is indicated in status bit 0.
The EPP operates on a two-phase cycle. First, the host selects the register within the device for
subsequent operations. Second, the host performs a series of read and/or write byte operations to the
selected register. Four operations are supported on the EPP: Address Write, Data Write, Address
Read, and Data Read. All operations on the EPP device are performed asynchronously.
11.2.7.1.
EPP Version 1.9 Operation
The EPP read/write operation can be completed under the following conditions:
a. If nWait is active low, the read cycle (nWrite inactive high, nDStrb/nAStrb active low) or write cycle
(nWrite active low, nDStrb/nAStrb active low) starts, proceeds normally, and is completed when nWait
goes inactive high.
b. If nWait is inactive high, the read/write cycle cannot start. It must wait until nWait changes to active
low, at which time it starts is as described above.
11.2.7.2.
EPP Version 1.7 Operation
The EPP read/write cycle can start without checking whether nWait is active or inactive. Once the
read/write cycle starts, however, it does not finish until nWait changes from active low to inactive high.