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From: F1.EGS@ISUMVS.BITNET ("E. G. Schnoebelen")
Newsgroups: comp.sys.apple
Subject: SOS-ProDOS compatability
Message-ID: <8611102040.AA04271@ucbvax.Berkeley.EDU>
Date: Wed, 5-Nov-86 23:01:32 EST
Article-I.D.: ucbvax.8611102040.AA04271
Posted: Wed Nov  5 23:01:32 1986
Date-Received: Tue, 11-Nov-86 06:27:46 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 24

Re: Apple /// SOS and Apple // ProDOS

Software written on one of the operating systems will not run on the
other without a change in the format of the operating system calls
and a recompilation on the other OS.

ProDOS uses a 4 byte sequence in this format :
              JSR MLI          ; goto the OS entry point.
              <OS opcode>      ; byte specifying what is to be done.

SOS on the other hand uses a two byte sequence as follows:
              BRK             ;Jump to the OS through the interrupt routine.
              <OS Opcode>     ; byte specifying the OS operation.

The OS opcodes are the same between SOS and ProDOS, so the only changes
needed to switch OS's is to change the JSR MLI to a BRK or visa-versa.

The above can be found in the ProDOS Technical Reference Manual ( I don't
remember what pages, It's not here ) and in the SOS Technical Reference
Manual ( I was remembering from SOS 1.3 ).

Eric Schnoebelen
F1.EGS%ISUMVS.BITNET@WISCVM.ARPA
Standard Disclaimers apply -- I work for no one, except maybe myself.