Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!apple!mattd
From: mattd@Apple.COM (Matt Deatherage)
Newsgroups: comp.sys.apple
Subject: Re: JMP/JML revisited...
Message-ID: <30977@apple.Apple.COM>
Date: 17 May 89 23:33:39 GMT
References: <1187@orbit.UUCP>
Organization: Apple Computer Inc, Cupertino, CA
Lines: 47

>Matt, the JML instruction is absolute indirect.  You may only:
>   JML (16-bit_address)
>
>It then takes the three-byte address from the 16-bit address in the current
>program bank.
>
>There is a form of the JMP instruction that is absolute long.  Here's an
>outline of some JMP forms and why they can't be changed to JML by the
>assembler:
>
>absolute                 JMP addr16           JML is only absolute indirect
>absolute long            JMP addr24           JML is only absolute indirect
>absolute indirect        JMP (addr16)         JML requires a 3rd byte at
>                                              addr16+2 for the new program
>                                              bank
>
>Also, there is no absolute indexed indirect version of JML, which is one
>reason why JMP (addr16,X) can't be changed.  The other reason is that as in
>the case of absolute indirect, JML requires a 3rd byte at addr16+2 for the new
>program bank.
>
>UUCP: {uunet!rosevax, amdahl!bungia, chinet, killer}!orbit!pnet51!shawn
>INET: shawn@pnet51.cts.com

(Sorry I lost the "he writes" line.)

This simply isn't true.  Most references I've seen say JMP and JML ar
alternate forms of the same opcode, with JML forcing long addressing.  The Eyes
and Lichty books list JML as an alternate form of JMP for all instances where
the addressing being jumped through (absolute or effective) is three bytes
long.

I'm not saying you don't have a reference that says what you say; I'm saying
that common usage is exactly the opposite.  Common usage doesn't limit JML
to one form, making it different from JMP.  In fact, assemble some code and
then list it in the monitor, and see what opcode it puts beside it.


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