I guess that the bracket+ports that does not work has non-standar cabling... remember these usually came with the motherboards, I speculate that you simply don't have it's matching mobo... 😀
nothing to worry, just don't use it anymore!

and COM1 / COM A are the same... just A&B become 1&2 and vice versa only a matter of how the manufacturer likes to name the ports 😎

keropi wrote:

I guess that the bracket+ports that does not work has non-standar cabling... remember these usually came with the motherboards, I speculate that you simply don't have it's matching mobo... 😀
nothing to worry, just don't use it anymore!

and COM1 / COM A are the same... just A&B become 1&2 and vice versa only a matter of how the manufacturer likes to name the ports 😎

Ah, yes of course! 😀 These bracket+ports gadgets are intended to be used for the specific mobo they came shipped with. It's interesting how these 2 gadgets appear to work on some other mobos - perhaps there are not too many differing Com Port standards?

Yesterday I changed a pinout for a similar thing, but with two USB ports.
You should not just plug these on any mobo and hope it works, there is a real danger for damaging things as you can easily get 12 Volt on the wrong contacts.

gerwin wrote:

Yesterday I changed a pinout for a similar thing, but with two USB ports.
You should not just plug these on any mobo and hope it works, there is a real danger for damaging things as you can easily get 12 Volt on the wrong contacts.

Damn. I didn't realise about this danger. Do you know roughly what the probability is, that damage could occur? Also, what would get damaged - the mobo? Other components on the mobo? Or just the mouse?

Do you know how can I use these com port headers on these old 486 mobos more safely? (They are not "proper" Com Ports which stick out of the back of the mobo, but instead they are groups of 10 pins sticking somewhere out of the middle of the mobo.)

Thanks. 😀

The pinout of those RS232 connector cables is not standardized, but most mainboards have the same layout (using the simplest straightforward method to match the cable leads to both ends).
It's possible that the non-working cable uses the correct pinout, but some of the wires are broken.

The naming of the ports correlates with the assignment of resources (I/O address, IRQ):

1Port | I/O | IRQ
2----+------+-----
3COM1 | 3F8 | 4
4COM2 | 2F8 | 3
5COM3 | 3E8 | 4
6COM4 | 2E8 | 3

On many boards and interface cards you can freely assign different resources to the ports (e.g. swapping COM1 and COM2 by exchanging the values). What matters is that most programs expect the resources for a given COM port to be set to the values in the table above.

About the danger of frying something when using a mismatched cable: I've used random cables on random mainboards for years and the worst that happened was that the port simply didn't work as long as the wrong cable was plugged in. This doesn't mean it's completely without risk, as the outcome depends on the electrical design of the port and the peripheral you connect to it. Theoretically anything can happen, ranging from blown SMD fuses to mainboards going up in flames.

I've blown the serial level converter on a mainboard once by shorting output to output, so yes, bad things can happen. Though only connecting a mouse might be not so dangerous in that case.

If the brackes came shipped with the used mainboard it does not neccessarily mean they fit, the seller might not have known about the difference and maybe just put random cables into the box.

5u3 wrote:

About the danger of frying something when using a mismatched cable: I've used random cables on random mainboards for years and the worst that happened was that the port simply didn't work as long as the wrong cable was plugged in. This doesn't mean it's completely without risk, as the outcome depends on the electrical design of the port and the peripheral you connect to it. Theoretically anything can happen, ranging from blown SMD fuses to mainboards going up in flames.

You are lucky. My main retro system has no more COM ports, I disabled them in the BIOS since they don't work anymore. They got broken after regularly attaching an older digital camera to them, sometimes while the system was on. Another system had a broken LPT port after using it to control some relays/transistors...

Can anyone help with a Com 1 issue. I'm running Win 7 and the software is Multicom (for a MFJ 1728 Node Controller for Amateur Radio). Multicom is a DOS based program and I am able to run program through DosBox. I can't get the program (Multicom) to recognize my Com 1 port. I have configured the Com 1 port (in Multicom) with the same settings as are in Windows 7 but the program says NO CONNECT. I am using a 25 pin cable (on node controller) to 9 pin on computer. I bought this node controller new back in the day (mid to late 1990's) and it worked fine back then and has been boxed up ever since. The node controller appears to be working fine, it is receiving data (I can see this from the led lights on the front) but from the node controller to the computer is where it appears to be the issue. I am only showing one com port & one LPT 1 on the computer and my mouse is connected via USB port. The only thing I am running on this machine is the node controller. I would appreciate any and all help you can offer.

https://blog.adafruit.com/2009/11/16/fixing-m … m-port-dongles/

This was mentioned by me in other topic but being bears to say again with evidence that you need to check your by pull back the black hood after undoing the nut studs.

Cheers,

Thanks Pentiumspeed, I will check but I believe this port (in general) works through windows 7 just not when I'm running DosBox program. I should have checked this first but will verify.

Once you know, look for another one that is different and try that. If you don't have extra, you can re-arrange by soldering. Otherwise keep collecting more mystery cables till you find one.

Cheers,

pentiumspeed wrote on 2020-03-11, 19:54:

pull back the black hood after undoing the nut studs.

In general, I find this is advice to live by.

SirNickity wrote on 2020-03-11, 23:29:

pentiumspeed wrote on 2020-03-11, 19:54:

pull back the black hood after undoing the nut studs.

In general, I find this is advice to live by.

Hehehe. I get your meaning but what else can I say more politer than that?

Cheers,

the port is working on its own in Win 7 but doesn't through DosBox