Basically the YIS-503III R is just another Yamaha MSX2, like the YIS-503II. The differences are: Russian keyboard layout, networkinterface and a built-in CP/M. Maybe there are more things changed but I am not a hardware specialist so I can't tell.
The networkinterface is a 60-pins module of the same type as used in other Yamaha MSX-computers like the CX5M and the YIS305. The electronic schema can be found here.
I extracted the roms so other people can make study of them. As far as I know these roms are copyrighted by Yamaha so please don't use them for any commercial purpose.
| MSX2.ROM | |
| MSX2EXT.ROM | |
| 16 kB ROM | Built-in CP/M, starts with _CPM |
| NETWORK ROM | Networkinterface |
To compare, the roms of the YIS805R (teachercomputer, 2 diskdrives):
| MSX2.ROM | |
| MSX2EXT.ROM | |
| DISK.ROM | Diskrom, built-in floppy-controller |
| NETWORK ROM | Networkinterface |
| PAINTER.ROM |
According to Stanislav the roms MSX2.ROM and MSX2EXT.ROM are identical. Basically the rom of the networkinterface is the same but can differ a little because of the 2K RAM it contains. The hardware of the interface is the same. Only the studentcomputers have the built-in CP/M network operatingsystem, the teachercomputer could boot from a CP/M floppy.
Working on it...