CIO's initialization routine.
The main CIO routine (includes the following routines).
STATUS and special requests routine.
GET routine (GET character and GET record).
PUT routine (PUT character and PUT record).
Return from CIO with the status in the Y register.
Return from CIO with the status in ICSTAZ (35).
Compute the handler entry point using HATABS (794) and COMTAB (59081).
Jump indirectly to the device handler. An indirect jump, in this case, means fooling the 6502 into thinking that the address you want to jump to is actually the one you want to RTS to. This involves playing with the stack and is a pretty neat trick you may want to look at.
Find a particular device in the handler address table.
This is a table of offsets into the handler entry point table for the desired device. It is used to find the correct vector for the given command.
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