rs232 handler need for a custom interface

Hi all,

Around 1990 before I had a blackbox Kaj de Vos made a custom RS232 and SIO2PC interface for me.

As far as I know it required a special handler in SpartaDos.
But I can't find it.
I've attached two pictures, front and back. I don't have any clue what it is, as long as its working

The reason I'm looking for the driver is because I want to connect the RS232 interface to a RS232 to Ethernet converter I found on eBay.
So I won't be needing the AtariMax interface to connect to the internet.

I hope someone can help me out.

regards,

Louis