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Square D SY/MAX 400 PLC Connection Problem
Unable to go online with Sy/Mate Plus software to download program

I recently was tasked with migrating an old (working) industrial station that is using a Square D SY/MAX 400 PLC.

The company I work for has a copy of the Sy/Mate Plus Ver. 2.06 programming software from a similar project many, many years ago but the last person who worked with this software has been retired for quite some time.

I am trying to download the program so I can look through the logic and re-write it for a different controller, preferably to an Allen Bradley (my bread and butter brand) or Modicon (closest successor to Square D?) if it would be easier.

Can anyone who has worked with this sort of controller give me some recommendations? The software is DOS based so I have tried running it with DOSBox on Win 8.1, on a Win95 VM with serial pass-through and on an old IBM Thinkpad that has a dual-boot with Win2000 and Win98; all to no avail. I keep receiving the connection error when I try to go online with the controller.

Literature and online resources are limited regarding this controller and software suite and even the docs I found didn't provide the details I was looking for. I have not worked with this particular controller/software before so any input/tips would be great. Thanks.

By Curt Wuollet on 5 April, 2016 - 8:53 am

Not much help, but I worked for a while with symax at a foundry. They outsourced a conversion and the contractor used Seimens because it would work with the old remote IO. It was bloody, but it worked when it was done. It wouldn't be my choice, but I mention it because there might be some tools or an established migration path. You have to remember that a lot of the old stuff was Koyo under the covers, so perhaps they share some lineage. I thought the Symax was easier to work with than Step anything.


By Steve Myres on 5 April, 2016 - 11:49 am

Square-D sold Koyo stuff? That's definitely news to me (though a lot of things are!) The only stuff I ever knew them to private-label were their micro PLC's, which were Idec IIRC.

Not sure to be honest, all I know is I cannot get the software to connect to it and it is driving me crazy. I am actually very surprised that I cannot find any useful information about the subject anywhere.

By Curt Wuollet on 5 April, 2016 - 11:08 pm

I could be wrong, but just about everybody did. It surprised me when I could get Step 5 spares at Automation Direct.

I don't really understand why, I would think the Siemens and GEs of the world could make a PLC. Perhaps patent issues or something like that.

I actually backed up old, old, gear (TI?, Step3?) with an audio tape recorder (Google Kansas City Standard) and an interface from AD. Must have been one step up from paper tape.


Using WIN98 in DOS mode should eliminate any issues with the OS handling serial data in a timely fashion; also check the buffering in the 16550 or whatever UART the laptop uses. This may be an issue with the RS-232 driver hardware on the laptops you are using. Logic levels shift with drive capability for different chipsets. I've had laptops refuse to connect to field devices when another laptop would, same OS, same software. Another potential issue is the Modem Control Signals, Allen-Bradley PICs were notoriously finicky (something to do with timing). DOS software can be installed on a bootable USB via the HP USBDisk utility, and that will allow you to use different laptops' serial ports until you (hopefully) find one that works.

1 out of 1 members thought this post was helpful...

I assume that you are trying to recover the project to save time and effort. Once you have a copy (printout) you can reprogram in any plc you favor. Schneider did have a conversion package a few years back but that is likely gone the way of DOS.

I have lots of stuff for SQD plcs. Software, both "key" and "non key" plus documentation. The last time that I used the software you had to use a "slow dos" application to slow the PC as the SQD software would not run on computers faster than 25MHz.

SQD had plcs in lots of meat packing plants and airport applications. Check around your area. Somebody may still have a PC with the s/w installed.

I can send you what I have if you provide email.

EdM, didn't think of trying to get a dos bootable usb and trying different laptops, that is an interesting idea. Just to confirm if anyone knows, the cable I should be using is RS232 or RS485?

Brian, you're right, trying for the same exact functionality in a more up-to-date package, so I think the easiest way to do it is to view the existing logic and migrate it over to my plc of choice. My main problem thus far has been connecting to the PLC itself and I'm not certain if its because I have the wrong software/cable or because of an OS/compatibility issue but I am determined to figure it out. As far as the dos speed that is an interesting point, I didn't know that.

Also, I am sure anything you send over will be very helpful, thank you for your help and my email is

I currently use SyMax\400 software almost everyday. The software I use is SFW374, I've heard of the Symate software just never used it.
The cable you need to use a RS-422. If you do a basic search for SyMax plcs you should find most of the manuals online (someone scanned them in) on Schneider's site somewhere.

I use DOSBox in Windows 7 64 bit and I have no issues going online with plc. Make sure you slow down DOSBox rate to a value less that 10000 cycles (I use 3000-5000).

There is a conversion upgrade path by Schneider, they will convert your old SyMax logic, swap the PLC and place interface modules in your remote racks so you could do a phased approach in either time or money.

Let me know if there is anything else I can help with...I didn't think anyone had SyMax left in the world :)

Thanks for the reply, I am currently trying DOSBox, a Win95 VM, a Win98 VM in VMWare Workstation 11 all on Win 8.1 and a very old IBM ThinkPad with dual boot Win 98 & Win2k. None of them work, I keep getting the same connection Error 74 - Response timeout, check cable connections. no matter what I try on every platform. The IBM has a native serial port and I am using an RS232 to USB adapter(prolific ftdi) on the other platforms. Between the RS232 side and the PLC I am using an RS232 to RS422/485 adapter.

The configuration I am using is the default which is COM1, 9600 baud, parity even, etc. I have tried with UART Transmit/receive turned all the way down or off, and I have tried changing the baud rate and the parity and most other combinations I could think of. I am also using SFW474 I believe, Sy/Mate Plus version 2.06.

What are your exact COM settings and program side settings?

What are your DOSBox settings/configuration?

Is there any specific procedure that you would recommend, step1 connect cable, step 2 power everything on, step 3 set config, etc?

I know this software should work because the reason I have it is its a remnant from when the controller was originally commissioned. I am also in the process of trying what Brian suggested and is also helping me with but I still have no luck with connecting.

Thanks in advance for your help.

Can you verify with any other device that your USB to RS-232 adapter through the RS-232 to RS-422 converter is working? The cable I use for SyMax is from NR&D. I have tried some brands of 232 to 422 converters that will not work with SyMax comms. I have found the powered converters work better than passive ones. Your com settings look ok.

If I remember correctly the only settings that I "had" to change in DOSBox was for the serial settings and a line to "mount" the SFW374 driectory so I could launch sfw374.exe. The serial setting is almost at the bottom of the config. Mine is "serial1=directserial realport:com1" (without the quotes). At the very bottom of the config I have "mount c c:\sfw374\". I created the SFW374 directory in the root of C: and this is were all the development software files reside as well as the plc programs and label files.

When I need to interface with a plc I launch DOSBox, mount the directory, run sfw374, take care of the security level, create the route to the plc, and go online. All of our plc's are on network , so all routing is through NIMs (network interface modules). According to the manual I suppose if you are connecting directly to the plc your "route" should be "NONE". Your "System Cards" probably is "ASYNC".

Came across this thread, currently working with a SyMax (have an XP laptop with WINMATE software).

We have been able to connect and upload (PLC to PC) the live programs for PDF printouts. However, it appears that we cannot upload the label files. I believe they reside only locally on drives, and are not actually stored on the PLC, but wanted to see if anyone could confirm that.