exxos's Atari, Amiga & retro forum

How do I set up a connection between two STs (STe and Mega STe) in order to test if the serial ports are working?
I was hoping I could type something on one computer and have it pop up on the other computer's screen using terminal software but I'm not getting anywhere (I've been previously told that it's just a matter of having the same port settings on both machines) but either I've misunderstood something with the settings, I'm using the wrong cable, or one/several of the serial ports are malfunctioning.

What I have confimed however is that the Mega STe "Modem 1" port is working, using the diagnostic cartridge and wiring up a a 9-pin D-sub female loopback plug (using the pinouts discussed here). The two other ports gave me various error messages with the same loopback plug, but at this stage I don't know if I should use a different loopback plug for those, or if indeed the ports are malfunctioning as I haven't been able to locate the pinouts for them.

I see no reason why my STe modem port isn't working (the computer has been working fine all along), but of course don't know this for sure. So could it be that I'm using the wrong cable? I have Exxos' diagnostic cable which I've been told is a nullmodem cable, and has the right connectors/genders at each end to allow for attaching between the two computers.

As this cable was meant to be used together with the Exxos diagnostic cartridge it's strange that I can't see the Mega STe output on the STe when I have the cartridge plugged into the Mega STe. Like I said, the MSTE "Modem 1" port checked out OK, so at least it should work with that port (I've tried all three).
As for software I've tried the VT52 terminal (TERMINAL.ACC from the language disk) as well as ConNect '95. I've also made sure the correct port has been selected using "Modem.CPX" in the MSTE control panel.

The simplest way to test is by connecting the MSTE and STE separately to a PC using the serial cable and booting with the diagnostic cart in.

Using a Terminal program (I use Teraterm) you can then see the serial port output on the PC. If you can select menu items and run them from the terminal, you are in reasonable shape as you are both sending and receiving.

My feeling it that whilst your cable might be fine for that purpose, going from MSTE to STE might not be suitable as in my experience not all null-modem cables are the same.

Pacman wrote: 03 May 2021 12:31 How do I set up a connection between two STs (STe and Mega STe) in order to test if the serial ports are working?

You need to use a null modem cable. Google “null modem” and have it show pictures. You need the 25 pin version. Note that the ones shown cross over all the hardware handshake lines to. It you turn off hardware handshake on both Atari’s all you need for a cable is pins 2 and three on each connector. Note 2 goes to 3 going both directions and you need pin 7 to 7. Set both Atari’s 9600, 8N1

rubber_jonnie wrote: 03 May 2021 12:43 The simplest way to test is by connecting the MSTE and STE separately to a PC using the serial cable and booting with the diagnostic cart in.

Using a Terminal program (I use Teraterm) you can then see the serial port output on the PC. If you can select menu items and run them from the terminal, you are in reasonable shape as you are both sending and receiving.

My feeling it that whilst your cable might be fine for that purpose, going from MSTE to STE might not be suitable as in my experience not all null-modem cables are the same.

Hmmm... that sounds plausible. I assumed the diagnostic cable followed a universal pinout, but seeing how many loopback connector pinouts there are it doesn't surprise me.
Can anyone confirm that the Exxos store's "diagnostic cable" is meant for connecting ST computers to PCs, and not to other STs?

I don't have a PC, and my Mac doesn't have a serial port, so the only other computer I can hook up to the MSTE is the STe.

PaulJ wrote: 03 May 2021 13:23

Pacman wrote: 03 May 2021 12:31 How do I set up a connection between two STs (STe and Mega STe) in order to test if the serial ports are working?

You need to use a null modem cable. Google “null modem” and have it show pictures. You need the 25 pin version. Note that the ones shown cross over all the hardware handshake lines to. It you turn off hardware handshake on both Atari’s all you need for a cable is pins 2 and three on each connector. Note 2 goes to 3 going both directions and you need pin 7 to 7. Set both Atari’s 9600, 8N1

I see there are several null modem cable configurations. Wikipedia tells of four:
1) no hardware handshaking
2) loopback handshaking
3) partial handshaking
4) full handshaking

I believe you're referring to the "no hardware handshaking" version as shown here: (image source: Wikipedia)

I understand this is the most basic setup that works, but would the "full handshaking" configuration be better suited for actually testing all aspects of my serial ports (pinout below), or are you saying that for an ST to another ST only the 3-wire pinout above will work? (image source: Wikipedia)

The MSTE has three 9 pin D-sub male connectors while the STe has a single 25-pin D-sub male connector.

Apart from the Exxos nullmodem cable (which physically fits between my two STs) I have a couple of normal serial cables (25-pin male to 9-pin female, used with modems in the past I believe) which only fits the MSTE end. All these cables appear moulded and I believe can't be opened to resolder the wires without damaging them and needing new connectors.

But I also have a short cable of the same type except the connectors can be opened, so I could use that as a conversion cable between either the Exxos cable or one of the standard serial cables instead of butchering the moulded ones.
I need to figure out the pinouts of them all first though....

It's slightly frustrating as I have a great null-modem cable that I got from a seller called Kenable on eBay.

It has 9 & 25 pin connections at both ends and works a treat, but it's currently in storage so I can't check it for you ARRRRGGGGGHHHH

Would it not be feasible to get a USB2Serial adaptor for your Mac?

Also, you can get null modem adaptors that fit in a chain with your serial cable, though you'd have to check to see what wiring it had.

Pacman wrote: 03 May 2021 16:13 Can anyone confirm that the Exxos store's "diagnostic cable" is meant for connecting ST computers to PCs, and not to other STs?

That should normally make no difference. You need a nullmodem cable when connecting two computers directly (whether PC or ST), and a "normal" cable when connecting the computer to a modem.

rubber_jonnie wrote: 03 May 2021 17:02 It's slightly frustrating as I have a great null-modem cable that I got from a seller called Kenable on eBay.

It has 9 & 25 pin connections at both ends and works a treat, but it's currently in storage so I can't check it for you ARRRRGGGGGHHHH

Would it not be feasible to get a USB2Serial adaptor for your Mac?

Also, you can get null modem adaptors that fit in a chain with your serial cable, though you'd have to check to see what wiring it had.

I'll figure it out in the end, but glad you wanted to help :)
I could probably get a USB to serial adapter, but I don't want to put too much money into this and it would mean ordering online in these lockdown times and waiting for a while.
I'm still a little confused about the various wiring schemes, but I think I'll start by checking which pin goes to where on my "normal" and "Exxos diagnostic" cables. I've studied some pinout diagrams online, and I see some that have different pins joined together on both ends meaning it won't be enough to just replace the connector/wiring at one end. In that case I hope I can cut open the moulded part so I can access the connectors and rewire them.
That short serial cable I have is too short to connect both computers together, so I figured it might do the job as an adapter together with one of the other cables.

thorsten.otto wrote: 03 May 2021 17:12

Pacman wrote: 03 May 2021 16:13 Can anyone confirm that the Exxos store's "diagnostic cable" is meant for connecting ST computers to PCs, and not to other STs?

That should normally make no difference. You need a nullmodem cable when connecting two computers directly (whether PC or ST), and a "normal" cable when connecting the computer to a modem.

Exactly what I thought, so this confuses me even more -why a connection between the two STs won't work with it.
I guess checking out the pinout first will help figure out why.

UPDATE: I'm done checking the first cable.
Here's the pinout of the Exxos diagnostic cable (for use with the Exxos diagnostic cartridge):
EDIT: Oops!!!! I got the pin names wrong.
This one should be correct: And here's what I believe is a standard serial cable which I had a couple of:

rubber_jonnie wrote: 03 May 2021 17:02 It's slightly frustrating as I have a great null-modem cable that I got from a seller called Kenable on eBay.

It has 9 & 25 pin connections at both ends and works a treat, but it's currently in storage so I can't check it for you ARRRRGGGGGHHHH

FWIW, I use the same Kenable double-ended nullmodem cable extensively with no problems, usually with my TT on one end and something else running the diag software on the other, and it always works great.

If you're attempting to talk between a MSTE and a ST Exxos's cable should work fine as is. It has a 9 pin on one end and a 25 on the other and it's a null modem cable. give it a try.

Strange..... very strange.
As posted earlier I got no response on either computer with that Exxos cable.

PS: I got the pin names wrong in my previous posting (the pinouts). It's correct now and I've added what I believe is a standard serial cable.