The is the OSI 65A serial monitor ROM
This is used primarily in the OSI C3 series but can also be found in OSI500 serial based systems.
This ROM can be used with different BOOT ROMs when located @ $FE00 or by itself as the only ROM in the system when located at $FF00. It expects the console ACIA at $FC00

Cmds 'R' reset,
     'P' <address> - dump data at supplied address until keypress
     'L' <address><data> - read hex data from acia until 'R' encountered
     'G' Go - set CPU value to the following:

         Execute address hi,lo @ $012E, $012F
         S Stack pointer    @ $012D
         K Processor status @ $012C
         A @ $012B
         X @ $012A
         Y @ $0129

