Computer Hope

Hardware => Hardware => Topic started by: neilw1 on May 12, 2011, 05:13:40 AM

Title: Help with 9 pin RS232 pins.
Post by: neilw1 on May 12, 2011, 05:13:40 AM

Hello,
I've got a plotter (well, it's a vinyl cutter), which is serial and according to the manual the pin-outs are as follow.
(http://static.allegro.cc/image/cache/d/a/da680c83106a53cb478067448a2b3b5d.png)

It looks to be as if they put '1' for RTS when really they meant '7'. However, that aside, is this a standard straight through cable because TX/RX are not crossed but I thought if it were straight through then 4/6 and 7/8 wouldn't be linked?

I'd rather just buy a cable, but this layout is confusing me :)

Thanks for any help in letting me know about this layout.

Title: Re: Help with 9 pin RS232 pins.
Post by: Geek-9pm on May 12, 2011, 06:17:33 AM

Early serial connector layouts  were defined by the computer maker.  If that was they way they did it, that was the way it worked. Standard layouts became standard later.
The layout you show in the picture is not exceptional at all.

Here is another almost the same.
http://www.diyha.co.uk/electronics/comm1.html
And with photos
http://www.google.com/search?q=9+pin+serial&hl=en&client=firefox-a&hs=yHq&rls=org.mozilla:en-US:official&prmd=ivns&tbm=isch&tbo=u&source=univ&sa=X&ei=Sc7LTbDjKZO4sAObjqToBg&ved=0CDIQsAQ&biw=853&bih=372
I like this one:
(http://t0.gstatic.com/images?q=tbn:ANd9GcQNozJcTnxdMAwSJP9wCZ2TmsfasyCJRJx1XaVnjfQ6o-NafSx9)

Title: Re: Help with 9 pin RS232 pins.
Post by: Computer_Commando on May 12, 2011, 10:42:32 AM

Read this:  http://www.camiresearch.com/Data_Com_Basics/RS232_standard.html
The manual is incorrect if it shows Tx on Computer connected to Tx on Plotter, same for Rx.  Tx is never connected to Tx & Rx is never connected to Rx, no matter what pin they are on.

Title: Re: Help with 9 pin RS232 pins.
Post by: Geek-9pm on May 12, 2011, 11:06:09 AM

Computer_Commando, That is a very good reference.
Does it apply to the question of the OP?
I respectfully disagree.
The manual he has is not for general applications. It is specific to just one product made some time ago. There was no rule that they had to observe conventions used by others. In fact, some other small computer makers at the time made the 9 ping assignments in their own way. It was chaos.
The diagram is consistence  with itself.It is for a special cable needed for that particular device. A technician would wire the cable exactly as shown. The cable does not care what you call the wires. The terms Tx and Rx are for reference.
Here is yet another reference that gives modern conventions.
http://www.lammertbies.nl/comm/cable/RS-232.html
But what the OP has is old assignment t for just one product.
But it there is any doubt, he needs to test the individual lines and find out what they are.