I know of 3 different motherboard serial header pinouts (and am sure there are more). Straight, staggered and a mix of those two, no matter what the board printing is.
First thing is find which board pin is ground, that is for pin 5 on the serial port back plate. Usually board pin 10 is not connected.

Here's an image of the board but not much other details.

also, details on this board: https://theretroweb.com/motherboards/s/zida-4dps

I confirm, COM headers on Tomato Zida 4DPS, can be a nightmare!
Before I figured out what was wrong with the three mice I tried on the com port, I went crazy!
In the end I had to redo the pinout of the com port cable one cable at a time 😂

Yes a little nightmare 😉 doesn't expected to have so many trouble for just a mice ...

ok I will tried repin. So, just to be sure, I will have to put the 1 of the cable to the 1 of the end connector for the board, the 2 of the cable to 2 of the connector? and so on ? simply that ?

geekretro wrote on 2025-01-28, 22:52:

Yes a little nightmare 😉 doesn't expected to have so many trouble for just a mice ...

ok I will tried repin. So, just to be sure, I will have to put the 1 of the cable to the 1 of the end connector for the board, the 2 of the cable to 2 of the connector? and so on ? simply that ?

Yes, good luck 😁

I received my cable, but no luck, so I repin from this cable db9 to header like 1 to 1, 2 to 2 and so on, but it doesn't work at all, oh well....

Chatgpt told me to inverse the 2 and the 3, but no chance.

Any chance you could have the correct pinout when you redo the pinout on your own board? perhaps you did not have anymore your board. The pins on the board doesn't seems to be accurate, seems mixed and without any logic. Thank you.

If I'm patient, I could buy a multimeter but I will need to learn how this works. But perhaps I will have to order a ISA card with serial ports if I don't find anything

In my case, I managed to recover the wiring of the com port mounted on the bracket, I isolated the wires from the ribbon cable, I cut them and reconnected them according to the motherboard pin-out

So you managed to connect from serial cable to IC 1 to 1, 2 to 2, 3 to 3 and so on? if you have other infos, it will be appreciated !

I have writed to "theretroweb" about this problem, someone told me there is 2 kinds of pinout, something I already know.

I'm starting to think that these com ports onboard are defects...

If you are good with a multimeter, you might use my SDT (Serial Debug Terminal)
it will let you raise/lower DTR & RTS, as well as send characters (and BREAK). It also
shows (in real time) the state of DSR, CTS , CD and RI

As you probe the pins, raise and lower DTR to identify that output pin - do the same with RTS
and then TXdata (use BREAK ON/OFF)

Once you know the outputs, connect a 1K resister from DTR to identify the DSR, CTS, CD and RI
pins (the on-screen display that mirrors what you are setting DTR to is the one)

After all that, you should have only 1 input left, connect TXdata with the 1k resistor and
it should mirror any characters you type!

Dave

ok I should ask my collegue on that, perhaps he will be best than me with multimeter, thank you for the hints!

There is nothing really special about the COM port headers with 4DPS, I have one myself and modified one generic com port bracket thingy for it. The pinout is pretty much always easy to figure out and wire the COM port accordingly.

With any motherboard, if you don't know the header pinout from the documentation etc., the number 1 pin is pretty much always marked on the silk screen. Then, find the ground pin (5) with multimeter and rest is easy to figure out.

The IDC connecor always connects the flat cable the same way, that is just the way that the IDC connector works. Flat cable wires are connected to IDC connector in this fashion:

1 2
3 4
5 6
7 8
9 10

So the second wire is connected to the first row and second column in the female IDC as depicted above. You have already figured out the pinout on the mobo, so now you can see that the second wire of the flat cable is actually connected to the pin 6. You need to solder this wire on the DB9 connector to the 6th pin that is the first pin on the bottom row of the connector. Third wire is connected to the number 2 pin, which you need to solder to the second pin on the DB9 connector next to the pin 1. And so forth.

You can clearly see that the connector pinout you posted doesn't work here.

Hi, I have repinned like this from serial cable to IDC, according to staggered style:

1-1
2-3
3-5
4-7
5-9
6-2
7-4
8-6
9-8

But it still doesn't work. I have a serial Microsoft mouse 2.1a with a ball, this mouse is working on another system pentium.

Maybe the com ports onboard are defect..

Yeah, that looks like a correct wiring for 4DPS and it should work.

It is possible that the IO chip is faulty, I've experienced it myself. Other possible factor is damage on mb such as a broken trace etc., so check the board visually for possible scratches near the com header and Winbond IO chip. Does the other onboard IO operate normally, such as IDE and floppy?

It could also be that your COM cable/bracet is faulty as it is possible that the flat cable is installed poorly to the IDC connector. You can pop the IDC connector open and re-install the cable again or try testing with another COM cable/bracket.

All other devices is good: IDE, Floppy, Cdrom, etc..

I have received my ISA card 8 bit with builtin serial and mouse still not working 😉 the bios detect the isa card and Com1 (after disable the ones onboard). In Dos, the utility MSD detect the Com1 from the isa card.

Perhaps it's the mouse version and the driver used: I have a Microsoft Serial 2.1a (with ball) and this mouse is functionnal on another system. So perhaps it's a problem with driver after all. I have tried many dos driver version: 6,02, 7.04, 8.20. Now I have download the 9.1 driver, I have test on dos based on the instructions Readme but no luck.
I will try in win95 there is a setup but I think I have already tested that...

Is there any trusted and compatible driver that could drive this mouse?

I'm running out of ideas, for this retro PC 😉

and another info: the 4DPS have a onboard ps/2 5-pin, perhaps this port is interfering with mouse detection? In win95, is it always detect a Ps2 mouse, so I Install manually de serial Microsoft without success.... the ps/2 port I can't disable it by bios.... but perhaps with a ps2 connector I could use instead a ps2 mouse. It's a possibility

I haven't had any issues with the PS/2 on my 4DPS, I just don't use it.

I don't use Win95 with any of my 486s, just pure DOS. Does your mouse work in DOS mode? If you can't get the mouse working with a separate IO card, the problem is somewhere else and if it works in DOS, you definitely have some sort of driver issue going on.

For DOS I use pretty much exclusively cutemouse and it should work just fine. And do not load any DOS driver for win95 desktop, let windows use its own.

The mouse isn't working in dos 6.22, with many versions of the driver. With cutemouse the driver loads at Com1 Irq4 (3f8) but when I start dosshell the mouse doesn't work. And with separate IO ISA Card, the mouse doesn't work more. In Dos, the diag tool MSD sees Com ports (1200 bauds), and when driver is loaded, it sees driver but say no mouse detected.

I suspect perhaps a "short" on the board, perhaps the way I installed the board in the case. Don't know if small short could interfere with serial ? or power supply don't send enough current to all devices?

Update: I have read a post about AT power connector corroded, I check mine and I clean them. After that, mouse was working ! but the onboard COM still not working but with ISA card the mouse is functionnal.

So COM are perhaps dead or still to know the correct pinout.