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From: shawn@pnet51.cts.com (Shawn Stanley)
Newsgroups: comp.sys.apple
Subject: Re: JMP/JML revisited...
Message-ID: <1187@orbit.UUCP>
Date: 17 May 89 03:26:07 GMT
Sender: root@orbit.UUCP
Organization: People-Net [pnet51], Minneapolis, MN.
Lines: 38

mattd@Apple.COM (Matt Deatherage) writes:
>In article <1135@orbit.UUCP> shawn@pnet51.cts.com (Shawn Stanley) writes:
>>Someone mentioned that a good assembler would change JMP to BRL during the
>>assembly.  (Actually, he said it would change JMP to JML, but we know what he
>>meant.  :-)
>
>No, I think he actually meant what he said.  The point was that any assembler
>worth it's salt is not so picky as to refuse to generate a long jump instruction
>(usually abbreviated JML) if you force long addressing on a JMP.  In other
>words, a good assembler should generate the same code for JMP >LongOffset as it
>would for JML LongOffset.
>
>(Now don't confuse my use of "offset" up there with thinking I really mean
>"branch".  I mean "jump".  I'm just testing y'all.)

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.

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