Information Technology Reference
In-Depth Information
Table 17.2
Byte-mode signals
Compatibility
signal na
me
Byte-mode name
In/Out
Description
HostClk
Out
Used as an acknowledgment signal. It is
pulsed low after each transferred byte.
STROBE
HostBusy
Out
It is set LOW to indicate that the host is
ready for nibble and set HIGH when the nib-
ble has been received.
AUTO
FEED
1284Active
Out
Set HIGH when the host is transferring data.
SELECT
INPUT
Out
Not used.
INIT
INIT
PtrClk
In
Indicates valid data byte. It is set LOW to
indicate that there is valid data on the data
lines and then set HIGH when the HostBusy
going high.
ACK
BUSY
PtrBusy
In
Busy status (for forward direction).
PE
AckDataReq
In
Same as
DataAvail
.
SELECT
Xflag
In
Not used.
In
Indicates that there is reverse data available.
ERROR
DataAvail
D0-D7
D0-D7
In/Out
Input/output data lines.
Valid data
Data
HostBusy
PtrClk
HostClk
Figure 17.5
Byte mode data transfer cycle
17.5 EPP
The enhanced parallel port (EPP) mode defines a standard bidirectional communications
mode and is used by many peripherals, such as CD-ROMs, tape drives, external hard disks
and so on.
The EPP protocol provides four types of data transfer cycles:
