Author Topic: RS232 Differences/Advantages between D-Sub 9 and 25  (Read 2643 times)

0 Members and 1 Guest are viewing this topic.

Offline giacomoTopic starter

  • Regular Contributor
  • *
  • Posts: 69
  • Country: it
RS232 Differences/Advantages between D-Sub 9 and 25
« on: April 20, 2021, 10:30:48 pm »
Hello everyone, i wanted to ask the difference/advantages between the RS232 that uses the D-Sub 25 pin connector and the 9 pin version
 

Online mariush

  • Super Contributor
  • ***
  • Posts: 4983
  • Country: ro
  • .
Re: RS232 Differences/Advantages between D-Sub 9 and 25
« Reply #1 on: April 20, 2021, 10:51:40 pm »
See the pinouts on this page, along with descriptions and text: https://www.virtual-serial-port.org/article/what-is-serial-port/rs232-pinout/

 
The following users thanked this post: giacomo

Offline TK

  • Super Contributor
  • ***
  • Posts: 1722
  • Country: us
  • I am a Systems Analyst who plays with Electronics
Re: RS232 Differences/Advantages between D-Sub 9 and 25
« Reply #2 on: April 20, 2021, 10:54:43 pm »
Hello everyone, i wanted to ask the difference/advantages between the RS232 that uses the D-Sub 25 pin connector and the 9 pin version
What devices are you connecting, what distance?
 

Offline giacomoTopic starter

  • Regular Contributor
  • *
  • Posts: 69
  • Country: it
Re: RS232 Differences/Advantages between D-Sub 9 and 25
« Reply #3 on: April 20, 2021, 11:00:37 pm »
I have some old instruments with the 25 pin connector, a 25 to 9 pin cable would do the job. Just a couple of meters.

It was just curiosity.
« Last Edit: April 20, 2021, 11:04:30 pm by giacomo »
 

Offline mvs

  • Frequent Contributor
  • **
  • Posts: 370
  • Country: de
Re: RS232 Differences/Advantages between D-Sub 9 and 25
« Reply #4 on: April 20, 2021, 11:15:26 pm »
RS232 is very old interface. DB25 connector was original one with some additional signals and reserved pins. DB9 came later, with a rise of the pesonal computers in eighties.
8250 and 16550 UARTs, and obviously later SuperIO chips were able to serve only 8 signals used in DB9. DB25 connectors were used for physical compatibility only and had no advanteges over DB9. I doubt you will find any working equipment with RS232 that use more signals then DB9 can carry.
 
The following users thanked this post: giacomo

Offline giacomoTopic starter

  • Regular Contributor
  • *
  • Posts: 69
  • Country: it
Re: RS232 Differences/Advantages between D-Sub 9 and 25
« Reply #5 on: April 20, 2021, 11:26:44 pm »
Thank you guys

Would you have an use example for the secondary signals ?

From the article posted by mariush:

"They include secondary DTE, RTS, DCD, TxD, and RxD. The secondary signals are used to optionally connect DTE and DCE equipment."
« Last Edit: April 20, 2021, 11:30:17 pm by giacomo »
 

Offline T3sl4co1l

  • Super Contributor
  • ***
  • Posts: 21606
  • Country: us
  • Expert, Analog Electronics, PCB Layout, EMC
    • Seven Transistor Labs
Re: RS232 Differences/Advantages between D-Sub 9 and 25
« Reply #6 on: April 21, 2021, 12:24:15 am »
I don't think I've ever seen anything that used even half the pins in a DB-25 serial port.  Teletype maybe?  I don't know.  It's one of those odd standards that's so old, it's well, well outlived its original purpose.

As far as I know, when it comes to computers, at least since the...70s or so?, all serial signals are present in both, they are functionally identical.

So yep, just dimensions, and whatever cost the bigger connector adds.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 
The following users thanked this post: giacomo

Offline guenthert

  • Frequent Contributor
  • **
  • Posts: 706
  • Country: de
Re: RS232 Differences/Advantages between D-Sub 9 and 25
« Reply #7 on: April 21, 2021, 01:58:19 am »
Well, just because a given device has a DB-25 socket, unfortunately no conclusion can be made about its use.  The original IBM PC had (in addition to RS-232 signals), a current loop interface on its DB-25 socket.  I've seen computers (not necessarily 'PC's) which used DB-25 for parallel printers -- where typically a "centronics" (DB-36) socket has been used.  Apple even put SCSI on DB-25 sockets.
 
The following users thanked this post: giacomo

Online xrunner

  • Super Contributor
  • ***
  • Posts: 7496
  • Country: us
  • hp>Agilent>Keysight>???
Re: RS232 Differences/Advantages between D-Sub 9 and 25
« Reply #8 on: April 21, 2021, 02:33:14 am »
I still have a book somewhere ... I think it's titled "The RS-232 Solution" which told you how to interface RS-232 devices that didn't exactly conform to proper standards ...  :-DD
I told my friends I could teach them to be funny, but they all just laughed at me.
 
The following users thanked this post: giacomo

Offline giacomoTopic starter

  • Regular Contributor
  • *
  • Posts: 69
  • Country: it
Re: RS232 Differences/Advantages between D-Sub 9 and 25
« Reply #9 on: April 21, 2021, 02:36:18 am »
I still have a book somewhere ... I think it's titled "The RS-232 Solution" which told you how to interface RS-232 devices that didn't exactly conform to proper standards ...  :-DD

Is this one ?

https://jbretro.wordpress.com/2018/11/06/rs232/
« Last Edit: April 21, 2021, 02:40:51 am by giacomo »
 
The following users thanked this post: xrunner

Online xrunner

  • Super Contributor
  • ***
  • Posts: 7496
  • Country: us
  • hp>Agilent>Keysight>???
Re: RS232 Differences/Advantages between D-Sub 9 and 25
« Reply #10 on: April 21, 2021, 02:38:10 am »
I still have a book somewhere ... I think it's titled "The RS-232 Solution" which told you how to interface RS-232 devices that didn't exactly conform to proper standards ...  :-DD

Is this one ?

https://jbretro.wordpress.com/2018/11/06/rs232/

YES! I used it a fair amount back in the day.  ;)
I told my friends I could teach them to be funny, but they all just laughed at me.
 
The following users thanked this post: giacomo

Offline notsob

  • Frequent Contributor
  • **
  • Posts: 690
  • Country: au
Re: RS232 Differences/Advantages between D-Sub 9 and 25
« Reply #11 on: April 21, 2021, 03:27:58 am »
It took me a while to understand until I started working on synchronous communications over RS232 - that's where the DCE - DTE comes in force where the DCE is providing the clock source and then all the hand shaking control lines come into force
 
The following users thanked this post: xrunner, giacomo

Offline CaptDon

  • Super Contributor
  • ***
  • Posts: 1662
  • Country: is
Re: RS232 Differences/Advantages between D-Sub 9 and 25
« Reply #12 on: April 21, 2021, 02:08:34 pm »
Those 'extra' signals were very useful years ago when printers and modems were much slower. For instance the link between modem and computer could have been 9600 baud, but the phone line connection may have only run at 110 or 300 baud so some handshaking would be required. Also on printers such as the ThinkJet with serial comms. You could dump to the printer at 9600 but it couldn't print that fast so DTE/DCE was important. Also remember RS-232 is only one use for a 25 pin cable. How about hooking an external ZIP drive to the printer port? A 25 pin cable isn't only used for RS-232 standards.
Collector and repairer of vintage and not so vintage electronic gadgets and test equipment. What's the difference between a pizza and a musician? A pizza can feed a family of four!! Classically trained guitarist. Sound engineer.
 
The following users thanked this post: giacomo

Offline HB9EVI

  • Frequent Contributor
  • **
  • Posts: 722
  • Country: ch
Re: RS232 Differences/Advantages between D-Sub 9 and 25
« Reply #13 on: April 22, 2021, 04:53:32 am »
in the days before FTTH, DSL and LTE/5G we used dedicated modems with Dsub25 ports for dialup. Before the upcoming of NAS-routers like the Ascend MAX series, which were our first all-in-one (analog and ISDN) dialup solution, we had stacks of Elsa modem like the TLV.34. Of course they already didn't use any other signals than a common 9 pin DSub offered, but physically attached they were over bulky 25pin cables.

the fully wired 25pin Dsub cables were quite multi use; either for EIA232, parallel port like the interconnect to a zip drive, or old fashioned SCSI-2 for scanners or SCSI zip drives; to my memory the JAZ drives already used 50pin interconnects like they were used for HSSI as well

yea, the good old times; not that I wish me back the speeds of those days, but the web was at least still free of Google, FB and all those other creepy business makers; I miss these nerdy days of the internet
« Last Edit: April 22, 2021, 04:55:37 am by HB9EVI »
 

Offline wizard69

  • Super Contributor
  • ***
  • Posts: 1175
  • Country: us
Re: RS232 Differences/Advantages between D-Sub 9 and 25
« Reply #14 on: April 22, 2021, 05:20:58 am »
You would be better off finding the manuals for the instruments in question.    First to make sure the 25 pin connector is RS232 at all.   Then to make sure there isn't other information on the connector that has nothing to do with RS232.    In the industrial world you often find the connectors overloaded with other unrelated functions so that some pins might have analog signals, trigger inputs or what ever, that have nothing to do with RS232.    If you are lucky you will have Transmit, Receive and Ground.   

I have some old instruments with the 25 pin connector, a 25 to 9 pin cable would do the job. Just a couple of meters.

It was just curiosity.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf