You remember about 5 years ago, PC's had serial ports and parallel
ports.

Right now I've got a laptop and it only has USB. I've been looking
around for some sort of adapter device for converting USB to DE9 for
serial ports, and also USB to DB25 for parallel ports.

All over eBay, there's USB-to-parallel-port adapters that work as
follows:

There's a converter from USB to RS232 and it has a DE9 plug on the end
of it. From there you have a simple adapter that goes from DE9 to
DB25. Obviously, since the DB25 has 16 more pins than the DE9, I don't
see how this is possible. The only thing I can guess is that 16 of the
pins are "left dead". Here's an example of such a device:

http://cgi.ebay.ie/USB-To-Serial-COM-RS232-DB9-DB25-Cable-Adapter-UK_W0QQitemZ250254094497QQihZ015QQcategoryZ41995QQssPa
geNameZWDVWQQrdZ1QQcmdZViewItem

If you read the description, it openly proclaims that it can be used
for hooking up things like scanners and printers. Does anyone know
what's going on here? Is it trully possible to get a parallel port
from using this?

Also, there's a different device that claims to be a proper USB-to-
parallel adapter:

http://www.usbgear.net/item_157.html

What's the difference between them?

Tomás Ó hÉilidhe wrote:

>
http://cgi.ebay.ie/USB-To-Serial-COM-RS232-DB9-DB25-Cable-Adapter-UK_W0QQitemZ250254094497QQihZ015QQcategoryZ41995QQssPa
geNameZWDVWQQrdZ1QQcmdZViewItem

this is for RS-232 9 pin, and rs232 25 pin, if you also recall, original 
rs-232 was 25 pin, and many printer were RS-232.


> Also, there's a different device that claims to be a proper USB-to-
> parallel adapter:
> http://www.usbgear.net/item_157.html
> 
> What's the difference between them?

this sounds like a real db25 printer port, but the software is for older 
windows, so it may be worthless unless it has modern drivers.

Cheers Don...


-- 
Don McKenzie

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On Jun 3, 12:15=A0am, Don McKenzie <5...@2.5A> wrote:

> this sounds like a real db25 printer port, but the software is for older
> windows, so it may be worthless unless it has modern drivers.


How is a printer port different form a DB25 RS232 port? Do these
printer ports use something other than RS232?

Op Mon, 2 Jun 2008 16:21:17 -0700 (PDT) schreef Tomás Ó hÉilidhe:

> On Jun 3, 12:15 am, Don McKenzie <5...@2.5A> wrote:
> 
>> this sounds like a real db25 printer port, but the software is for older
>> windows, so it may be worthless unless it has modern drivers.
> 
> 
> How is a printer port different form a DB25 RS232 port? Do these
> printer ports use something other than RS232?

It's not without a reason that the DB25 printer port was called a
_parallel_ port instead of a _serial_ port (RS232) that had 25 pins
too at the time ;-)
-- 
Coos

On Jun 2, 6:21=A0pm, Tom=E1s =D3 h=C9ilidhe <t...@lavabit.com> wrote:
> On Jun 3, 12:15=A0am, Don McKenzie <5...@2.5A> wrote:
>
> > this sounds like a real db25 printer port, but the software is for older=

> > windows, so it may be worthless unless it has modern drivers.
>
> How is a printer port different form a DB25 RS232 port? Do these
> printer ports use something other than RS232?


Centronics style parallel ports (and the follow on IEEE 1284 ports)
are nothing at all like (RS-232) serial ports.  They just happen to
often use DB-25 ports on the backs of PCs.  Note that those are
basically always DB-25 *female* port, unlike serial ports which use
males connecters.  At the printer end, these often use the old
Centronics style connector (which were also occasionally used on the
host end of the connection, but the large size was often awkward).
See the second picture here:

http://en.wikipedia.org/wiki/Parallel_port

Unlike serial ports, parallel ports transmit data in, *ahem* parallel,
with some handshaking.  It was designed to be a cheap to implement
interface using TTL logic levels and minimal ports at both ends (eg.
no expensive UART).

RS-232 is defined with the 25 pin connector, but back in the AT days,
PC vendors started using the DB-9s to save space, since for async
serial communications, most of the RS-232 signals are useless, and you
can fit what you actually need in those nine pins.

The USB-to-serial dongles work OK (although driver issues abound for
some unknowable reason), so long as the serial device is, like a
modem, fairly tolerant of slow responses to the handshaking and flow
control signals.  A "real" serial port can often respond to a drop of
CTS in a handful of character times, while the USB serial ports can
have hundreds of bytes in buffers.  Also, some people use the flow
control signals on serial ports to control some device directly -
while on a "real" serial port these can be modified very quickly, the
USB serial devices may require milliseconds to propagate the change to
the actual device.  But within those constraints, they work passably
well.  There are some USB serial devices which claim to be better on
some, or all, of those parameters, so if you need something like that,
you may want to do some research.

The USB to parallel port adapters, OTOH, tend to not be direct
replacements for "real" parallel ports, and are typically useful only
for driving parallel printers.  Many people who have used the parallel
port as a cheap DIO port to control something have had to change with
the demise of real parallel ports.

Note that "real" parallel exist on PCI, and PCIe(!!) cards, and in
PCMCIA (aka CardBus) versions as well, which you can add to most PCs.
You can also add "real" PCI, PCIe and PCMCIA serial ports as well.

Tomás Ó hÉilidhe wrote:
> On Jun 3, 12:15 am, Don McKenzie <5...@2.5A> wrote:
> 
>> this sounds like a real db25 printer port, but the software is for older
>> windows, so it may be worthless unless it has modern drivers.
> 
> 
> How is a printer port different form a DB25 RS232 port? Do these
> printer ports use something other than RS232?

yes, RS-232 in the old days was +/- 12V DB-25, then DB-9 later.

Parallel or Centronics was .8V to 2.4V, or TTL signals. DB-25, or 
Centronics blue connector.

Modern versions take some liberties, but basically if you plug RS-232 
serial into a TTL printer, it will blow something up.

The only protection for DB-25's was the polarity of the plugs, which I 
forget for the moment. Someone will remember if it is required I'm sure.

Cheers Don...






-- 
Don McKenzie

Site Map:            http://www.dontronics.com/sitemap
E-Mail Contact Page: http://www.dontronics.com/email

Intelligent 2.83" AMOLED with touch screen for micros:
http://www.dontronics-shop.com/product.php?productid=16699

r...@yahoo.com wrote:
> On Jun 2, 6:21 pm, Tomás Ó hÉilidhe <t...@lavabit.com> wrote:
>> On Jun 3, 12:15 am, Don McKenzie <5...@2.5A> wrote:
>>
>>> this sounds like a real db25 printer port, but the software is for older
>>> windows, so it may be worthless unless it has modern drivers.
>> How is a printer port different form a DB25 RS232 port? Do these
>> printer ports use something other than RS232?
> 
> 
> Centronics style parallel ports (and the follow on IEEE 1284 ports)
> are nothing at all like (RS-232) serial ports.  They just happen to
> often use DB-25 ports on the backs of PCs.  Note that those are

snip---

yes, that's a much better answer than the abbreviated one I gave. :-)

Don...


-- 
Don McKenzie

Site Map:            http://www.dontronics.com/sitemap
E-Mail Contact Page: http://www.dontronics.com/email

Intelligent 2.83" AMOLED with touch screen for micros:
http://www.dontronics-shop.com/product.php?productid=16699

OK so here's what I understand so far:

* DB25 is nothing more than a connector, it can be used with different
kinds of transmission protocol
* Serial ports use the RS232 protocol
* Parallel ports use the IEEE 1284 protocol

Serial ports have a DE9, and parallel ports have a DB25.

Now I've been told that serial ports can use a DB25, which is a 25 pin
connector. When I don't understand about this though is how you can
have an adapter that goes from DE9 to DB25.. ? I mean how can 9 pins
suddenly become 25 pins? Are the extra 16 pins left dead?

If the extra pins are left dead then how could this adapter possibly
have a use? I mean if a device is using a DB25 for serial
communication then I presume it must need the extra pins, otherwise
it'd be using a DE9, right?

Tomás Ó hÉilidhe wrote:
> OK so here's what I understand so far:
> 
> * DB25 is nothing more than a connector, it can be used with different
> kinds of transmission protocol

The DB-25 male is a serial port.
     DB-25 female is a parallel port.

> * Serial ports use the RS232 protocol
> * Parallel ports use the IEEE 1284 protocol

This all started with the IBM PC years ago, long before 1284 was even 
thought of.

> 
> Serial ports have a DE9, and parallel ports have a DB25.

> 
> Now I've been told that serial ports can use a DB25, which is a 25 pin
> connector. When I don't understand about this though is how you can
> have an adapter that goes from DE9 to DB25.. ?

http://www.jaykang.com/db9fetodbmam.html

  I mean how can 9 pins
> suddenly become 25 pins? Are the extra 16 pins left dead?
Yes
> 
> If the extra pins are left dead then how could this adapter possibly
> have a use? I mean if a device is using a DB25 for serial
> communication then I presume it must need the extra pins, otherwise
> it'd be using a DE9, right?

Its obvious that you are very young.

This has been around for years, August 12,1981 to be exact.
http://en.wikipedia.org/wiki/IBM_PC

The original question about USB parallel ports was if the USB can 
replace a "real" parallel port.

The answer is no.


Why, you ask !!

Well, thats a homework assignment for the student(you). :-)

donald

On Jun 3, 4:30=A0am, donald <Don...@dontdoithere.com> wrote:

> > If the extra pins are left dead then how could this adapter possibly
> > have a use? I mean if a device is using a DB25 for serial
> > communication then I presume it must need the extra pins, otherwise
> > it'd be using a DE9, right?
>
> Its obvious that you are very young.
>
> This has been around for years, August 12,1981 to be exact.http://en.wikip=
edia.org/wiki/IBM_PC


Still I don't see how a 25-pin plug can become a 9-pin plug?

What happens to the extra signals on the 16 dead pins?

If there's no signals on these pins to begin with, then why does the
advice use a DB25 instead of a DE9 in the first place?


> The original question about USB parallel ports was if the USB can
> replace a "real" parallel port.
>
> The answer is no.
>
> Why, you ask !!
>
> Well, thats a homework assignment for the student(you). :-)


Why do you say that the answer is no? USB is a hell of a lot faster
than even the most advanced parallel port (IEEE 1284), so it seems to
me that this can be done perfectly if you have:

    * A microcontroller inside the adapter that does the job of
converting USB signals to parallel port signals
    * A device driver for the PC which fools the computer into
thinking it has a fully-fledged parallel port