Question I think my 25pin to 9pin serial wiring is wrong

Myronazz

Commendable
Sep 5, 2016
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Hello,

Apologies if I posted in the wrong section, moderators feel free to move my thread to a more appropriate topic.
So here is the thing, i've been trying to get my dial-up modem to work for days, my dialling box pops up and then ends up with error 630, which has something to do with the modem, after trying alot of things (even reverting back to Windows 98 to make sure I have a correct operating system for my driver) and same results, until it hit me, what if my 25-pin to 9pin serial adapter is wrongly wired, I took out my multi-meter and ran a continuty check to trace where each pins heads off to, here are the results

(Edit: Here is a table to make reading a bit easier)


Is this the right wiring for a modem, also my cable says null modem on it, not sure what it could mean by null

Thank you, if I do indeed have the wrong wiring, it would be extremely helpful if you could send me some kind of diagram that shows me where each pin is supposed to connect so I can rewire it, thank you!
 
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kanewolf

Titan
Moderator
Serial can be tricky. A commercial DB25 to DB9 adapter should be straight through. Then if needed a null modem can be added (IMO). That pinout looks like it has a null modem built-in because of the pin 2 to pin 2 and pin 3 to pin 3. Look at the transmit and receive pinouts in the Wikipedia table. A pin 2 to pin 2 would be a crossover of transmit and receive.
 

Myronazz

Commendable
Sep 5, 2016
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Serial can be tricky. A commercial DB25 to DB9 adapter should be straight through. Then if needed a null modem can be added (IMO). That pinout looks like it has a null modem built-in because of the pin 2 to pin 2 and pin 3 to pin 3. Look at the transmit and receive pinouts in the Wikipedia table. A pin 2 to pin 2 would be a crossover of transmit and receive.
So... what do you mean by strait through? Like pin 1 to pin 1, pin 2 to pin 2, and so on and so forth?

Do you suggest that I change it to that pinout?
 

kanewolf

Titan
Moderator
So... what do you mean by strait through? Like pin 1 to pin 1, pin 2 to pin 2, and so on and so forth?

Do you suggest that I change it to that pinout?
Look at the table I linked. Straight through would be just what is shown in the DB25 column and the DB9 column
DB25 -> DB9
2 -> 3
3 -> 2
20 -> 4
8 -> 1
6 -> 6
22 -> 9
4 -> 7
5 -> 8
7 -> 5
 

Myronazz

Commendable
Sep 5, 2016
185
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Look at the table I linked. Straight through would be just what is shown in the DB25 column and the DB9 column
DB25 -> DB9
2 -> 3
3 -> 2
20 -> 4
8 -> 1
6 -> 6
22 -> 9
4 -> 7
5 -> 8
7 -> 5
Clearly different from what I have, before I bring out the soldering iron and waste 2 hours trying to figure out what wire is what and resoldering everything, you think that there is a chance that it'll work? or slim one?
 

Myronazz

Commendable
Sep 5, 2016
185
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It looks like I will have to buy a new cable, I could rewire it but unfortunately for me there isn't wires for every pin, I need the DB25's 5th pin to be wired to to DB9's 8th pin, but there isn't wiring for the 5th pin at all, which makes this impossible if i'm not mistaken
 
The old days and the hassle of serial connectors. So spoiled by USB cables that just work in any ports.

Many times I know you had to wire pins together on the db25 side to makes this work. The where signal pins that the db9 did not support so you hooked 2 pin directly to each other on the db25. It was some signal the modem wanted that you had to fake because the db9 could not produce it.

I know I used to have a fancy little patch board with db9 and db25 and I could put short wires between until I got this figured out. It is still in some box in the garage I suspect.

I think the new problem would be finding a actual telephone line you could hook a modem to. Many of the things you find are a form of VoIP and do not have the bandwidth to carry modem/fax data.
 

Myronazz

Commendable
Sep 5, 2016
185
2
1,695
3
The old days and the hassle of serial connectors. So spoiled by USB cables that just work in any ports.

Many times I know you had to wire pins together on the db25 side to makes this work. The where signal pins that the db9 did not support so you hooked 2 pin directly to each other on the db25. It was some signal the modem wanted that you had to fake because the db9 could not produce it.

I know I used to have a fancy little patch board with db9 and db25 and I could put short wires between until I got this figured out. It is still in some box in the garage I suspect.

I think the new problem would be finding a actual telephone line you could hook a modem to. Many of the things you find are a form of VoIP and do not have the bandwidth to carry modem/fax data.
I have a classic analogue telephone line, they are still extremely common here in the UK because cable Internet is still kinda expensive, in fact I have a classmate who switched from cable to DSL because of costs

Im going to order another serial cable! but this time I sent the seller a message to verify it has the wiring I want, because I dont want to buy another wrong cable lol, I already bought 3 of them and they are all wrong!!! So I definately understand what you mean by hassle XD

I tried doing the same thing as your patch panel trick, except I tried inserting a male jumper wire to the cable female end, and then insert the female end of the jumper wire directly to the laptop's serial port but unfortunately that didnt work because my female jumper wire holes are too small to fit into the pins of the serial port :( such a shame it would be cool ti get it working like that
 
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Myronazz

Commendable
Sep 5, 2016
185
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DSL is still broadband, we talking about 56kbps dial-up right? I grimace at home long a typical web page takes to load.
Yes DSL is still broadband, he was just saying that getting dial-up to work over a VoIP telephone line instead of analogue one is hard, I just want to connect using dial-up one last time before the last service in my area dies, so not really worried about speeds, although that service that is still up supports accelerated dial-up (97 kbps) and so does my modem, so I guess it will be a bit more bearable XD
 

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