Constructing a null modem

I have recuperated two rs232c cables form old mouses.

The connection shema is given notably here
https://en.wikipedia.org/wiki/Null_modem

The RS232C side is molded, so i can't see what is wire 1, wire 2 etc

The other side inside the mouse nds on soe small connector, with 9 pins inline.
The color scheme for both cables is different.

If i look at that inner connectror from the contacts side,cable hanging down, how do i count the contacts from left to right or the other way?

@JosDuchIt

Much depends on what you'll use it for.
Our serial device supports 3 wire and 7 wire protocols.
There's also 5 wire, which is 7 wire with a few connections hardwired.

3 wire is transmit, receive, and ground.
To make a NULL cable connect ground to ground,
transmit to receive
receive to transmit.

This works for no handshaking, and XON XOFF handshaking.

The additional wires offer hardware handshaking, I'm sure you can look those up if needed.


Back to your question, if your mouse cables don't have the wires for hardware handshaking, you will be limited to 3 wire modes.

This picture is a MALE connector.
http://wiki.robotz.com/images/c/ce/Serialdb9pinouts.gif

You'll need a meter or something to figure out which wires connect to which pins. A small paperclip is handy for metering female connectors

@LyleHaze

It is not the principle for realising a null modem nor the numbering of the pins on a RS232C connector that are the problem.

Question is if i cut open the cable and see a lot of colored wires which is which? Indeed i have no direct access to the inners of that moulded connector.

I do have acces though to the 9 pin in line PCB connectors that i pulled out of the mouse's PCB.

Question is: how is their numbering scheme? (the colors are different but that is not even the main problem: how are the pins of the PCB connector related to the RS232 connector?

These small PCB connectors are some 1.7 cm wdth, light brown, hane one side with 2 heightened thickings and the contacts at the other side;

When i look at this contacts side with the colored wires down, is the numbering starting from left to right or from right to left?

This is the only answer i relly need

Having had a closer look on those Mouse pcb connectors they don't seem to be standardised, one has 8 contacts, the other one 9.
I'll disconnect them and measure the colorr codes out with a multimeter,

Result: only one out of three does not have broken wires on the essential 2, 3 and 5 contacts.The colors are not standardised : all three differ.

Luckily i got hold of two female RS232C connectors that are not molded.

@JosDuchIt

I try to give as complete an answer as possible.
Not just for you, but also for others who are reading this post who might also want to know how to do that.

I DID mention at the end of my post that you'll need a meter to figure out which wire goes to each pin.

After telling me that I did not answer your question, I see you went right on to do exactly what I suggested. Good for you.

Next time, I'll just keep to myself and let you figure it out.

@LyleHaze

My apolopgies if my answer seemed inappropriate,
I can see now why that is hpw you feel about it.

It was not my intention to be rude, I try to explain:

Before posting my first question i had tried to use the multimeter with a needle and did not get contacts. So in your answer i just looked (too fast) if i got the info i thought i needed about left to right or right to left ordering of pins. This occured probably because i had searched the internet about mull modems allready: i skipped that info and what followed too unfortunately.

In my second mail i just wanted to be very clear about what (i thought) i "really" needed, not anything else. At that moment i was puzzled with not getting results with the needle and thought it had to do with the PCB connector whose openings were still smaller.

I overlooked the paperclip suggestion, but believe me or not, took this up in a thread about testing Power Supply Units,
and it is really a good suggestion because the contacts work far better than with a needle and you can clamp one testing probe between the arms of the clip.

My third mail explained the results and i was still not aware you made that paperclip suggestion.


It is now nearly 3 weeks that i struggl to bring back to life my two Sam's which failed on me at the same moment.

I do use the Amiga as my main computer and losing both was and still is a very stressfull situation.

Please be assured i fully appreciate your and any help i get.
I'll read answers more carefully in the future.

Thanks for pointing out what annoyed you, and giving me the ooportunitity, i hope, to straighten things out/

Some days I think I should not be allowed on the internet.

I hope the damage is not permanent.

For others seeking information on NULL modem cables and Amigas, try this
http://wiki.amigaos.net/wiki/Advanced_Serial_Debugging_Guide

Roman wrote it, I had the first pass edits, many others have contributed as well.
RELIABLE terminal software is crucial, and I use one that is older than the hills, has a few warts, but it super reliable. it's called "Term"

details follow that link.

Yes, a paperclip is quite useful, as it can also clamp the probe tip. I keep a couple bent that way in my desk.

I also wrote Sentinel X-Logger, which allows Gen X Amigas to capture and save their own serial debug without a second computer.. but this is getting too far off topic.

Peace

@LyleHaze

Thank you for the most interesting link. This was exactly what i am after now: detect if it is the PSU or the mobo of the sam440ep that is affected.

I did build a null modem with no handshaking. from a serial cable with 2 connectors that could be opened and rewired, With my hands not as stable, as i would like any more, opening soldering and closing the connectors again took me nearly 3/4 hour.


I hope non handshaking null modem will work? else i'll have to restart the procedure :(


My SAM 460ex works again , but here too the learning curve was steep and scary as i did buy both SAM's ready boxed and OS installed. Scary also because the new 500 GB HD that i bought consumed too much power and produced read & write errors all over the place. I bought a SATA to USB docking station now with its own power supply and will use it as an external backup device.
I am working now with an old 40 GB HD (and or a 80 GB one) that i got from my neighbour.

Today i'll try to copy the sys partition to the 500 GB HD, next i'll copy my incomplete :(( backup to this drive, and i'll start feeling somewhat safe again.

@JosDuchIt
In the event you plan to try your null modem cable, you might want a shell command like echo2debug.lha at OS4Depot to see if your cable is working.

@xenic
Thanks for the hint
At the moment i have no way of making a script run on tha "dead" sam440ep. I can only rely on debugging info that u-boot might provide allready when trying to boot the machine.

I don't think i can test the nullmodem from the working Sam460ex only ?
I have also read the link provided byLylehaze
http://wiki.amigaos.net/wiki/Advanced_Serial_Debugging_Guide
My conclusion is that the nullmodem will not help me right now:

On powering on, & booting nothing appears on the screen , the HD led only flickers just once , then nothing. So i don't have the opportunity to put u-boot in serial output mode.
Is this right or do i miss something?

My PSU tester has just arrived and my hope is that problems are due to the power unit and not the motherboard. We'll see tomorrow

non-handshaking (aka 3 wire) is _usually_ the best or only way to go with Amigas.

On classic systems, handshaking is optional, software controlled.
On the X1000, I think 3 wire is the only way.

But some (pc-related) systems can't seem to get down to 3 wire unless some jumpers are added, they seem to have the hardware handshaking permanently enabled. So until you've passed a test, I can only say "maybe".

MIDI over serial is 3 wire only as well, which some may know is where I spend most of my time.

Testing a null cable CAN be done with just one computer.. IF you can jump TX to RX at the other end of the cable. Then everything that goes out should come right back. Note: This test will NOT tell you if it's a straight or null cable, the test works the same on both cable types.

Also note: If your term software has "local echo" turned ON, you'll see two characters for every one you type. This is expected, not broken.

I have no direct experience with SAM serial, so you'll have to verify things for yourself.

Good Luck,
Lyle

@LyleHaze
The only OS4 NG hardware I've had that was a complete 9 pin serial port was my µA1. I used it with a dialup modem using hardware hand-shaking. I was really disappointed when I got my SAM440 and discovered that it had a 3 wire serial port. I had to lower the speed of my dialup modem and use souftware hand-shaking. As far as I know, all the NG hardware since the original AmigaOnes have been 3 wire.