Null Modem Cable

[TallGuyinIT]

Really dumb question, but I am stuck and the staff at my local computer store cannot help.

I am trying to transfer files from my old PC to my new PC using the File Transfer Wizard in Windows XP. Both are stand alone PCs - not on a network. I cannot get the 2-PCs to link.

Here is my question. The wizard says to use a null modem cable. I have a standard cable with female DB9 connections at each end plugged into both com ports. Do I need a DB9 male to female null modem connector on one of the ends? I am not certain if having the female connectors on each end automatically makes the cable a null modem - or if I still need some type of converter.

 

[Frank4d]

You need a female connector on both ends and cable wired:
1&6 to 4
2 to 3
3 to 2
4 to 1&6
5-5
7-8
8-7
pin 9 = don't care

 

[georgewel]

They make null modem adapters. Basically all you are doing is making the receive signal pin from one unit go the the transmitt pin of the other computer and vica-versa.

 

[edfair]

Just a small addition. You are making the receive signal and handshake pins connect to the transmit signal and handshake pins.
The null modem adapter that you would use on one end of your cable does the switching you need.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[Bozz]

It might be worth getting a "LapLink" parallel cable if the local store does one. Parallel transfer is much faster.

Ian Boys
DTE Systems Ltd

 

[mrmomaz1234]

I've used the Laplink program (old, but still works) and it's cable and it works like a charm. As an aside, the program works great even on 1 pc to move files around.

 

[paparazi]

TallGuyinIT
Being the "hands on" sort of person that I am, I would say:
just remove your old hard drive (two side covers, four screws)
Piggy back it as a slave to either a CDrom or Hard drive on: Primary/Secondary channel of the new PC
Give the drive a molex power connector
Boot up
Possibly reboot after detection
Copy files across

This process takes about 5 minutes (plus time to copy files) is easy, but best thing, it costs nothing to do as you already have all the hardware to make it work.
Oh yeh! and a hell of a lot quicker to transfer your files! that could be crucial if you are like me and have 20gigs plus of photo's and music.
Martin


We like members to GIVE and not just TAKE.
Participate and help others.

 

[Baldrian]

Hi guys. I am new here so please dont yell at me.

I have a similar problem to the one described by TallGuyinIT who started the thread. I know taking the disk out is the easy and quick solution, but it is NOT satisfactory. The first reason is that I have 3 disks and a CD-player/writer in there already. The second reason is that this is not the way I want to do it. There is always a workaround, but the reason for asking on a forum is normally to find out how to do stuff, not to find out how to avoid doing it. At least this is normally the case for me. Now, to my problem.......:

I am (just for the fun of it) trying to connect two not exactly brand new comps. One is a Pentium 2 MMX 233, and the other I am not entirely sure, but it is a Pentium of some sort, maybe a 150 MHz (maybe a 100 MHz actually as it runs on 66*1,5). Anyway they both are a lot better then the PCs I have used for this earlier (typically 286 and 386 comps). The idea was to use a null modem cable and try out all the old games that I never had the hardware to run properly at the time. So I started by getting hold of a cable with female DB25 plugs in both ends. Now, this cable was wired completely wrong, but after 3 hours of soldering, I had a cabble that should work. (did 2/3, 3/2, 4/5, 5/4, 7/7, 6/20, 20/6, and then I short circuited pin 6 and 8 on both sides.

This is the standard cable for PC to PC transfer acording to Microsoft, and its supposed to be this cable that was shipped with LapLink Pro 4 (its laplink Pro 4 I am currently using to try to connect, have also tried interlnk/intersvr). But it still wont work. So what do I do? After testing the cable manually with a multimeter (measuring the resistance), I started testing the internal bracket cables. They are ok. All my cables have connection where they should and not where they shouldn't. Hm, next question: Does the controller work? Aparently it does. When reconnecting the original DB 9 male bracket I can install a mouse on COM2, so it had to be my bracket or its cable right? But how do I explain the fact that this bracket works on the other PC? In short, both brackets (I have one DB 25 male on each PC) work with my mouse on the Pentium 233 machine, but neither work with the other PC (I've tried both COM1 and COM2). At the same time the DB 9 male bracket seems to work fine on even COM2 on the difficult PC.

I have now found another cable connection scheme. I think its the old so-called 3 wire solution where you fake handshakes by short circuiting pin 4 to pin 5, and then pin 6 to pin 8 AND pin 20 on the same end. Then you do the same on the otherside. Thus, you in effect connect only pin 2, 3 and 7. And they go to pin 3, 2 and 7, respectively. Is there any chance that this may work after the problems I describe?? Of course I can just try, but my hands are not as steady as they used to be, and my eyes aren't all too good either..... 3 more hours of soldering tiny duppedits does not temp me if its not likely to work anyway..... Any ideas folks????? I bet I have tried this b4 I get any replies ))

 

[Bozz]

If you cross 4 to 5 and 6 to 20 then you get no handshaking. That means that there is no control over the flow of data and you may loose data or have errors. If you do use this cable keep the baud rates low and you might be OK. Don't forget, serial transfer is sloooooow anyway, it might be unusable at low baud rates.

The reason that I suggested using the yellow parallel cable is that it works with the direct cable connect capabilities of Windows and maintains a reasonable data transfer rate.

I'd get 2 of the cheapest network cards available and a crossover cable and network the PC's if at all possible. It's really not that difficult.

Ian Boys
DTE Systems Ltd

 

[edfair]

There are 2 kinds of internal M/B to d9 connector cables and 2 kinds of M/B to D25 cables. It sounds like you may have mixed versions.
The IDHeader is numbered 1 to 10 , odds on left, even on right, pin 1 at the stripe.
First type pins 1 to 9 of the IDH connect to pins 1 to 9 of the D9 and pins 8,3,2,20,7,6,4,5 and 22 of the D25.
Second type pins 1 to 9 connect to 1,6,2,7,3,8,4,9,5 of the D9 and 8,6,3,4,2,5,20,22, and 7 of the D25.


Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[Baldrian]

Hi again

To boss:
It should be apparent that this is not a good solution for me. I am not concerned about the transfer speed. I wa3nt to use it for the old dos games, and for that it is good enough..... if it works.... And just to drive home my point.... the the cable and connections that I described is the setup that microsoft say one should use exactly for direct cable transfers......

Then to edfair:

On my bracket there is no pin 9. That is; there is nothing connected to pin 9. The connectors on my motherboard (there are nine of them) route as follows:
1 to 8
2 to 3
3 to 2
4 to 20
5 to 7
6 to 6
7 to 4
8 to 5
9 to 22

The first number on each line is on the motherboard, and the second is on my DB25 male connector known as COM2.

Now, this connection is correct. I know that because I can use this bracket including cable on my other computer. And the one that was initially on my other computer is equal. Connecting anything to pin 1 or pin 9 on the DB25 female bracket would be a folly. There is no signal from there to the computer. I take it you are talking about the motherboard connections. Is that what you describe as IDHeader? All those pins are numbered on my card, so sorting them out is no prob. They are numbered as follows (ON THE CARD):

2 4 6 8
1 3 5 7 9

the plug that should fit on to this connector is pinned:

1 3 5 7 9
2 4 6 8

So after reaading your post again, I se that we agree this far. SO I connected the cable going from DB25 female to the other DB25 female like I stated in my earlier post:

2 to 3
3 to 2
4 to 5
5 to 4
6 and 8 to 20
7 to 7
and finally 20 to 6 an 8

This *should* work!!!! All pages I have found regarding null-modem cables are lines up like this. This is also the setup of the cable that came with LapLink pro (or so people say at least). It may be true that this is an overkill for transfering files, but even if it is overkill it should work with programs that support handshaking (I assume LapLink and interlink does). I mean this cable is referred to as a LapLink cable fgs!

My problem now is that the COM2 IDH does not work if I connect it to a DB25 male bracket. If connected to a DB9 male bracket I can easily hook up a mouse to the COM2. no problem. Why should there be a difference???

Baldrian

 

[Baldrian]

Ok. I think I get it EdFair......
I am using the wrong IDH layout.....

If the IDH on this PC is of the other type I'll have to rewirer the LapLink cable into (the cable between the 2 puters):

2 to 6
3 to 3
4 to 22
5 to 20
6 to 4
7 to 2
20 to 5

And then short 6 and 8 on one side and short 5 and 8 on the other.... Should that be correct??

Baldrian

 

[edfair]

Too early in the day to figure this out. Wasn't a problem to copy the documentation.

Better to resolve the M/B to bracket issues and use a standard laplink cable.

Simple way to figure which layout your board uses is to see what M/B pin is signal ground. Will be either 5 or 9.

Suspect that your 25 that doesn't work is the other type.

The 1-9 to 1-9 adapter is swappable with the 25pin that connects 8,3,2,... The 1,6,2...9pin is swappable with the 8,6,3...25 pin adapter.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[Baldrian]

I know its better to fix it on the inside, but I can't... The connections on that end is covered with solid plastic thats melted on. I cant get it off if I want to even. Is there a chance to burn the motherboard if I use the wrong layout?? And how do I find out what pin is ground? use a multimeter on the chassis to se what pin connects to it??


Btw.... I can check the layout of the DB9 brackets that work..... That way I'll know...... Thanks a lot for the help, I'll let you know if it works

Baldrian

 

[edfair]

1 to 9 and matching 8,3,2 have pin 5 of the header as ground.
The other sets have pin 9 as ground.
When you get done the 9 pin you'll connect to the outside world will have pin 3 at -12 (more or less) in respect to pin 5. The 25 pin bracket will be pin 2 with respect to pin 7.

You won't hurt anything if you use the wrong one. It just doesn't work.

You could also have brackets that were designed to work with ATIO cards. They may or may not be wired to different standards.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[Baldrian]

Hey dude..... It works!

I used the "wrong" set of connections from the IDH to the DB25 on one of the sides, so I had to modify the null-modem cable as follows. I connected (the first number is on the side that worked al the time):
8 to 4
3 to 7
2 to 2
20 to 3
7 to 22
6 to 4
4 to 6
5 to 20

On the first side I shorted 6 and 8 like normall but on the other end I shorted 3 and 8. Then it all work like a charm

Thanks a bundle

Baldrian