Well.... The "decsystem10 System Reference Manual (DEC-10-XSRMA-A-D) - available online: http://bitsavers.org/www.computer.museum.uq.edu.au/pdf/DEC-10-XSRMA-A-D%20D… has a definition for the -10 side of the interface on pages C-21 and following (page 365 of the PDF). It just specifies the I/O instructions and bits, there's no description of how it works. Still, that will help understand code that uses it; the complete ITS code is available. I couldn't find anything on the PDP-11 side of the interface; ITS' IOELEV > does define a "DLXCSR", and the bits in it, but ... it seems to be a memory location, not a register? The DL10 was used in two DEC system products, the DC76 Asynchronous Communication System, and the DN87 and DN87S Universal Communication System Front Ends. I couldn't find any documentation on the former, but complete prints for the latter are available: http://www.bitsavers.org/pdf/dec/pdp10/periph/MP00068_DN87_Universal_Comm_S… http://www.bitsavers.org/pdf/dec/pdp10/periph/MP00109_DN87S_Universal_Comm_… It includes a complete set of prints for the DL10. From this, and also from: http://pdp-10.trailing-edge.com/bb-d549g-sb/01/boot11.mem.html it appears that the PDP-11's connected to the DL10 have a special console which has a cable which goes to the DL10 which allows the PDP-10 to start and stop the PDP-11; the PDP-11's UNIBUS runs into the DL10 and is plugged into the DL10. Anyway, it's going to be some hard work to create a DL10 programming manual done. Noel