I've been reading this thread with some interest. Some observations:
1. The parallel port signals are a standard. Within the limits of that
standard it doesn't matter what kind of equipment is driving it, i.e., a
laptop will work just as well and supply the same driving capability as the
desktop. If performance varies with different computers then either the
interface or the machine fails to comply with the standard. Given the
standard chip sets used for such things these days, I'd blame the radio
interface, not the computer, if things don't work.
2. The Inspiron 8100 provides an ECP-capable parallel port. The IEEE 1284
signal spec requires that such a port be capable of sourcing 2.4v at 14ma.
3. Even if the printer port was strictly TTL signal levels, it would (by
spec) source at least 3.6v at 400 ua -- which translates to a dropping
resistor of 7.5k to the base of the NPN transistor used for switching.
4. I've don't think that I've ever burnt out a TTL gate by shorting the
output. Within their signal ranges they are difficult to destroy.
5. All of this means that if the port was damaged it was probably due to
the application of either negative or higher than normal voltage -- not bad
software or an incorrect dropping resistor value. This could easily happen
if a ground wire was temporarily disconnected leaving a path through the
gate for a small AC or DC voltage.
This was all determined by using sources easily available on the web. At
the same time, I have never used the parallel port to interface to my radios
as my first interfacing was with NT and I now use only Win2k or WinXP. My
interfacing is using the serial ports. For that I either use MAX232 EIA
level converters or open collector transistors with 2.2k base dropping
resistors.
I would suggest that if you're going to use a modern printer port to
interface for CW and the like that you go to the BIOS setup and select
"standard" or "unidirectional" for the printer port type.
73,
Mike WA0SXV
|