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Re: [vox-tech] more newbie questions
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Re: [vox-tech] more newbie questions

On Fri, 19 Apr 2002, Joey Karalius wrote:
> I have an extra serial port (9-pin), and I was looking for a 9-pin to 
> 25-pin cable.  That was when I ran across these serial to USB cables 
> which looked pretty cool, especially since I have extra USB ports. 
> (Henry, I'll take you up on your offer for the cable.  Let me know when 
> and where to get it...)

I would expect the USB to 9-pin serial are for USB to 9-pin serial, not
9-pin serial to USB. You also need to ensure there is kernel usb support
for a device like that adapter.

I have *never* tried to use a USB to "normal (9-pin/25-pin) serial
connector within Linux. I do not know if Linux even has support for such
USB devices. Others on this list may have more info on this.  Even if it
is supported, some com programs may have problems with using "non-standard

Going with a "standard serial port" is usually the easiest path and a
9-pin Serial connector with a 9-pin serial to 25 pin serial is often the
better choice (suggested by the previous poster.)

It is a good bet that any "male" 9 or 25 pin connectors on the back of
your computer are Serial. (Often 2 ports and next to each other, sometimes
one is used by a mouse. If your mouse has a 9 pin connector it is likely a
normal serial mouse and is using a "standard serial port" while if the
mouse connector is round it is more likely a PS/2 style mouse and is using
a "different kind of serial port" introduced by IBM ages ago that often
used a different IRQ (12) and io port from the "standard serial ports".

If you have just one female 25 pin port, that is likely the parallel port,
though if you have more than one, the second may be another parallel port
or possibly a SCSI port or some other port.

> A followup question:  Since the 25-pin SP connection is the same as the 
> PP connection, can I hook my PP ZIP drive to the SP, and my SP modem to 
> the PP?  When is a serial port not a parallel port, and vice versa? 

Just because the number of pins appears the same (25-pin db25
connector) for serial and parallel, does not mean you can use parallel
devices on Serial ports or vice versa. You may find some older SCSI ports
that are 25-pin and also use the DB25 ports as well.

Mixing different ports using different data exchange porotocols (SCSI,
Parallel, Serial) is a bad idea as many use different signalling
voltage. Not only will the cable connectors not do what you want with the
devices (unless trying to break them is the intent) but you run the risk
of damaging the devices and/or the ports on the machine.

- Just because something "fits" another thing does not mean that the two
things ahould necessarily be connected. ;-)

Also, you should note the parallel port on the back of your computer is a
female db25 connector while 25-pion serial and 9-pin serial are db25 and
db9 connectors that are male. One useful part to this is to make it easier
to know which is which just by looking at them.

With the above noted, there have been devices made that can hook to
parallel or serial ports, but they are very specialized andfrequently had
spcial switches you needed to flip for which kind of port you were using.

The IOMega ZipPlus SCSI/Parallel drive can work on DB25 SCSI connectors
*or* DB25 printer ports. Similar devices (often older) offered something
similar for Parallel and Serial, but they are rare.

> I've got the ZIP drive-to-printer hookup on my parallel port, and want 
> to use my scanner as well, but I understand that daisy-chaining these 
> things slows down performance. 

Assuming you can get it to work. Have you made your scanner work over a
parellel port in Linux?

> If I expand my port selection with another card, do I need to get a PP
> card for PP devices, and SP for SP devices? (I mean, if the shoe
> fits...) ;)  I just want to understand a little more 'bout the
> hardware.

Yes, different cards for different devices. You can often but "multi-port
io cards" that have 2 srial ports and 1 parallel port. Be carefule when
you buy them. Make sure you have choices for IRQs. 

Also, look at your free IRQ and io ports. 

$ cat /proc/interrupts
$ cat /proc/ioports

Serial com ports each need their own IRQ (unless you get "special serial
port addressing cards" which often need kernel support/os
support. Frequent assignments for com ports:
COM1  = /dev/ttyS0  : IRQ4, io 0x03f8
COM2 =  /dev/ttyS1  : IRQ3, io 0x02f8
COM1  = /dev/ttyS2  : IRQ(2/9) or 5 or 10 or 11 or 12*, io 0x03e8
COM2 =  /dev/ttyS3  : IRQ(2/9) or 5 or 10 or 11 or 12*, io 0x02e8

12* is often used by a mouse if a PS/2 mouse and other IRQ may be in use
by sound cards or other devices.

Serious problems will exist when you try to have devices "share IRQ" or
"share io ports" when they are not designed with this in mind. When you
wor with ISA cards this is especially important. (PCI cards seem to do a
better job of resource sharing.)

Ones I use for my 4 com ports:
COM1  = /dev/ttyS0  : IRQ4, io 0x03f8
COM2 =  /dev/ttyS1  : IRQ3, io 0x02f8
COM1  = /dev/ttyS2  : IRQ(2/9), io 0x03e8
COM2 =  /dev/ttyS3  : IRQ5, io 0x02e8

If adding a second parallel port, it will also need its own IRQ and io
port. When you examine the contents of /proc/interrupts and /proc/ioports
you can try to choose an IRQ and  port available on the card, and also
availble in the olist.

Last, just because you get a card with 2 serial and 1 parallel, does not
mean that you have to enable all of them. You can often disable what you
do not need and this is strongly suggested when you do not have enough IRQ
and ioports.

Wheee, a minihowto. Ok, it is not that well written. Never mind.

Version: 3.12
GCS/CM$/IT$/LS$/S/O$ !d--(++) !s !a+++(-----) C++$(++++) U++++$(+$) P+$>+++ 
L+++$(++) E W+++$(+) N+ o K w+$>++>+++ O-@ M+$ V-$>- !PS !PE Y+ !PGP
t@-(++) 5+@ X@ R- tv- b++ DI+++ D+ G--@ e+>++>++++ h(++)>+ r*>? z?
decode: http://www.ebb.org/ungeek/ about: http://www.geekcode.com/geek.html

> Thanks to all who helped...
> Joey
> Henry House wrote:
> > On Thu, Apr 18, 2002 at 01:44:44AM -0700, Joey Karalius wrote:
> > [...]
> > 
> >>2) I bought a serial external modem, and I'm shopping for a cable. It 
> >>has the 25-pin connection on the back and I think I want to go with the 
> >>USB to serial cable, since I have a couple empty USB ports.  Is there 
> >>any reason I can't go with that setup?
> >>
> > 
> > I take it your serial port is in use? In theory this should work fine, but
> > rather than search for such a non-standard and proabably costly cable (really
> > an adapter, since USB and RS232 serial are electrically different), I suggest
> > you peer inside your machine to see if there are pins for attaching an
> > additional serial port. Most modern machines have only one physical serial
> > port, but many system boards do have a controller for a second, which may be
> > brought into existance by installing a piece of metal containing a molded
> > serial port and a ribbon cable to plug into the mother board, the entire
> > device shaped to fit into a PCI slot in the back of the case.
> > 
> > I have a spare nine-pin to 25-pin serial cable in my office that I will
> > gladly give to yo if you like, if you decide to follow my suggestion.
> > 
> > 
> -- 
>                         ___
>          ____         /|   |
>     ||  /\   \       / |   |      ||                            ||
> <=====/  \   \=====|  |   |=======================================>
>     ||J\   \   \JK/\|  |   |JKJKJK||                            ||
>     ||KJ\   \   \/     |__ |KJKJKJ||   jwkaralius@ucdavis.edu   ||
>     ||JKJ\   \___\          /   /K||                            ||
>     ||KJKJ\   |   |    ____/___/KJ||   joeykaralius@yahoo.com   ||
>     ||JKJKJ|  |___|\   \   \JKJKJK||                            ||
>     ||KJKJ/   /   /J\   \___\JKJKJ||                            ||
> <=====|     /   /===\  /   /======================================>
>     ||  \___/___/     \/___/      ||                            ||
> _______________________________________________
> vox-tech mailing list
> vox-tech@lists.lugod.org
> http://lists.lugod.org/mailman/listinfo/vox-tech

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