I thought I had an old spec sheet for a Gateway 500, but I failed to locate it. I am fairly certain that it talked the Honeywell's proprietary DMCS protocol, but without the sheet, my memory could be faulty, because DMCS goes back to the late 1980's. IT was discontinued by Honeywell in 2000.
I did find one hand written notation related to DMCS, which was supposed to be a part number for a DMCS manual for their strip chart recorder.
DMCS Comm
date: 9/90
part number: EN1L-6106.
Good luck tracking down documents from the pre-pdf era.
I have a pdf file about specification of gateway model 500, but in this pdf there is not any detail for use gateway, from computer to connect DMCS network.
I have the complete manual for the Gateway 500 MANUAL 85-50-25-06 We do use the DMCS and I have been looking for spares since we are down to our last one.
There must be 300+ pages in the manual. Is there some specific section you would like. Chapter 1 Installiation,2 Communication Concepts,3 Protocols for Data Security,4 Establishing Communications and Testing,5 Recovering from communication Failures,6 Uploading and Downloading Device Databases,7 Service,8 Parts List.