moved to Parallel Port Signal Detail
Fig 10-2
DB-25
Pin
Driven by
Signal Name
Cent
Pin
1
Host
/Strobe
1
Tells the printer that data is available on Data 0-7. Pulse width must
be more than 0.5us. Must be high if Busy or /Acknowledge are also high. driven
by 7405 inverting open collector buffers, pulled to +5 volts via 4.7K resistors.
2
Host
Data 0
2
Data lines must be valid 0.5us before falling edge of Strobe
signal.
The Data Out pins were orginally driven by a 74LS374 octal latch, which could
source 2.6 mA and sink 24 mA. It is essential that the external device not
try to pull these lines to ground, as this might cause the 74LS374 to source
more current than it could handle without damage. Exception: bidirectional
printer ports allow the 74LS374 (or equivalent) driver chip to be tri-stated.
3
Host
Data 1
3
4
Host
Data 2
4
5
Host
Data 3
5
6
Host
Data 4
6
7
Host
Data 5
7
8
Host
Data 6
8
9
Host
Data 7
9
10
Printer
/Ack
10
Pulse width approx 3us. Asserted when Busy goes off or after data is
accepted. Also pulsed when printer comes on line after power on,
reset, or operater selects online mode. Inverted in Status Input
register
11
Printer
Busy
11
Indicates that the printer is busy. Asserted during reading of data,
printing, errors, and when offline.
12
Printer
Out of Paper
12
13
Printer
Select
13
High when printer is online.
14
Host
/Auto Feed
14
driven by 7405 inverting open collector buffers, pulled to +5 volts via
4.7K resistors.
15
Printer
/Error
32
16
Host
/Initialize
31
driven by 7405 inverting open collector buffers, pulled to +5 volts via
4.7K resistors. Double inverted from the control register.
17
Host
/Select Input
36
driven by 7405 inverting open collector buffers, pulled to +5 volts via
4.7K resistors.
18-35
Both
Ground
30
Ground returns
19-29
see also:
file: /Techref/io/parallel.htm,
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