On Jun 3, 4:01=A0am, Tom=E1s =D3 h=C9ilidhe <t...@lavabit.com> wrote:

> 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:
>
> =A0 =A0 * A microcontroller inside the adapter that does the job of
> converting USB signals to parallel port signals
> =A0 =A0 * A device driver for the PC which fools the computer into
> thinking it has a fully-fledged parallel port


Here's an example of what can be achieved:

http://cgi.ebay.ie/USB-2-0-to-SATA-IDE-Cable-Adapter-Serial-ATA-DVD-HDD-CD_W=
0QQitemZ270242517760QQihZ017QQcategoryZ74941QQssPageNameZWDVWQQrdZ1QQcmdZVie=
wItem

It's a device I bought off eBay a few days ago, it's for hooking up an
internal hard disk via USB (i.e. USB to IDE, or USB to SATA). I
haven't received it yet but I'll let you know how well it does or does
not work.

In article <9f9850f6-b1a5-4129-a8e9-1dba28a2b3f7
@d77g2000hsb.googlegroups.com>, Tomás Ó hÉilidhe says...
> 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

Define latency.

Robert
** Posted from http://www.teranews.com **

Coos Haak <c...@hccnet.nl> writes:
>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 ;-)


**in the IBM AT world**.

I've owned printers that took in serial data on DB25. There are still
to date industrial devices that can output data to a serial printer,
and exist serial interface printers with DB25 on them. 

The IBM PC/AT world introduced lots of new odd things that stick with
us to this day on the PC platform. 

Make sure that you specify which you are expecting, because there's
probably been something else the complete opposit that existed before,
and will exist again. 

=?ISO-8859-1?Q?Tom=E1s_=D3_h=C9ilidhe?= <t...@lavabit.com> writes:
>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?


Because the original used DB25. There are many standards that used DB25.
In the older days, there weren't quite so many different connectors as
there are now (while there were, but most of those are long dead, like
the DD50, or some of the 37-pin ISO connectors), so it got used for
many more different protocols and connectors.

Some of the protocols took over many of the 25 pins available. Some,
like RS-232 only used a handful of pins. Then the IBM PC/AT designers
felt like they wanted to have two serial ports in one card slot rather
than two in two slots, and used a non-standard DE9 with the reverse
(ie. male) pins to do it. Then it took off, and the whole world had to
go along with it, and the PC world expects a serial port to be a male
DE9 instead of the original female DB25.

Since RS-232 only used 9 pins anyway, it fit just right on it. The
other 16 pins go unused, and aren't connected to anything anyway. 

On Jun 2, 10:01=A0pm, Tom=E1s =D3 h=C9ilidhe <t...@lavabit.com> wrote:
> 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?


Again: The RS-232 standard is for a 25 pin plug, the DB-9 is a (non-
standard, although universally supported) subset of that.  When you
wire the two together, the other pins are left unconnected.  There
*are* signals defined for all 25 pins, but most are of no use for
async serial communications (which is almost all you see on PCs).
Some early PC manufacturers decided to use a DB-9 instead of a DB-25
because the brackets on ISA cards were only so big, and they could put
more stuff on it with the smaller connecter.  The DB-9 only carries
the signals useful for async.  You'll notice that even now many
external serial (async) modems have a DB-25, and you use a cable with
a DB-9 at one end and a DB-25 at the other - that simply wires the
adapter into the cable.

Note that it's possible to have RS-232 async communications with only
three wires (transmit, receive and ground), although that means giving
up some generally useful status information and using Xon/Xoff flow
control.

Note that if you actually had a synchronous serial device attached to
a synchronous serial port (*not* a normal PC async port), you would
need the full connecter, although not necessarily all 25 wires).


> 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:
>
> =A0 =A0 * A microcontroller inside the adapter that does the job of
> converting USB signals to parallel port signals
> =A0 =A0 * A device driver for the PC which fools the computer into
> thinking it has a fully-fledged parallel port


The latency across the USB link makes it impossible for all but the
slowest applications.  Nominally the date/strobe/acknowledge sequence
is about 10us (and visibility of the other handshake signals is closer
to 1us).  Full-Speed (12Mbps) USB will likely be a minimum of 1ms each
way, and Hi-Speed (480Mbps) USB 100us.  If you try to get cute by
moving the handshake logic out to the USB device itself, you end up
with something tied to a specific application - like the USB parallel
port printer devices you can get today.

Tomás Ó hÉilidhe wrote:
> On Jun 3, 4:30 am, 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.wikipedia.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?
> 

Google is your friend:

http://www.uwsg.indiana.edu/usail/peripherals/serial/rs232/

In the old days, long before you were born, computers were big machines, 
controlled using dumb terminals.  These dumb terminals were connected 
serially, either by wire or over a modem, and it was useful to have a 
number of extra signals (clocks, power, handshaking, etc.).  Thus DB25 
connectors were used.  Later, it was noticed that a lot of equipment 
could work fine with fewer signals, and the DB9 pinning became common. 
The DB25 connector was kept on PCs for backwards compatibility, but only 
the signals also found on the DB9 were implemented.

> 
>> 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
> 

You think this because you don't understand what "speed" and "faster" 
means.  The parallel port is faster than USB (even USB 2.0) in the same 
way that your PIC microcontroller is faster than your laptop.  See if 
you can figure this one out before others drop too many hints. 
Remember, throughput for bulk transfers is only one way to describe speed.

Op Tue, 03 Jun 2008 04:18:18 +0200 schreef Tomás Ó hÉilidhe  
<t...@lavabit.com>:
> 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

On a PC yes, but this is comp.arch.embedded: RS485 and CAN sometimes also  
use DB9.

Note that SATA and PCIe ports are also serial, but don't (or can't) use  
DB9 (or DB25).

> * 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?

Yes.  Or they can be used for a second serial port on the same connector.   
The mappings for the pins are all defined.

> 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?

Today, the world is littered with computer equipment factories.  Ideally  
you'd be using the connector that is optimally sized and abundant.  In the  
past that was DB25, but now that is DB9.


-- 
Gemaakt met Opera's revolutionaire e-mailprogramma:  
http://www.opera.com/mail/

On Mon, 2 Jun 2008 19:18:18 -0700 (PDT), Tomás Ó hÉilidhe
<t...@lavabit.com> 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

True

>* Serial ports use the RS232 protocol

Most serial ports use RS-232, but others might use RS-422/485
(balanced), RS-423 (unbalanced) or 20 mA current loop.

>* Parallel ports use the IEEE 1284 protocol

i.e 5 V TTL
>
>Serial ports have a DE9, and parallel ports have a DB25.

At least the RS-232C standard did not specify the connector and I am
not aware that some later revisions did that.

>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?

Usually only Tx, Rx, SGnd, RTS, CTS, DTR, DSR and possibly pGnd is
connected in these connectors. The rest is unused.

Paul

On Tue, 03 Jun 2008 11:37:21 +0300, Paul Keinanen <k...@sci.fi>
wrote:

>On Mon, 2 Jun 2008 19:18:18 -0700 (PDT), Tomás Ó hÉilidhe
><t...@lavabit.com> 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
Apple used to run SCSI thru a DB25 connector.

>
>True
>
>>* Serial ports use the RS232 protocol
>
>Most serial ports use RS-232, but others might use RS-422/485
>(balanced), RS-423 (unbalanced) or 20 mA current loop.
I have also seen serial connections on RJ45, RJ11(both the 4 & 6 pin
versions), and DEC used a MMJ which was an RJ11 with an offset tab,
and HP (I think) once used a DB9 shell with a custom 3 pin arrangment.
And wasn't it DG that used 6 or 8 pins in a line on one of their
terminals.

<snip>
-- 
ArarghMail806 at [drop the 'http://www.' from ->] http://www.arargh.com
BCET Basic Compiler Page: http://www.arargh.com/basic/index.html

To reply by email, remove the extra stuff from the reply address.

On Jun 3, 4:55 am, ArarghMail806NOS...@NOT.AT.Arargh.com wrote:
> Apple used to run SCSI thru a DB25 connector.


Not just Apple.  SCSI DB-25s were common on ZIP drives and on
scanners, and at least a few PC ISA SCSI adapters had DB-25s.  Getting
the right cable was always a challenge.

Frankly as far as parallel SCSI goes, you'd have an easier time
listing connecters that *haven't* been used.  (Yes, I'm exaggerating,
but only a little).


>I have also seen serial connections on RJ45...


Since we've mentioned Apple, they did serial on DIN-8s (similar to the
old "round" PC keyboard and mouse connectors) for a while.  TRS plugs
(AKA audio jack plugs) are also used by some small devices.  Lots of
old comm gear used screw terminal blocks rather than plugs.  Yes, it's
a mess...