ACME

         ...the ACME Crossassembler for Multiple Environments

                        --- 65816  support ---


This text contains information about the 65816-specific features of
ACME.


----------------------------------------------------------------------
Section:   Aliases for "long" JMPs and JSRs
----------------------------------------------------------------------

In addition to the mnemonics JMP and JSR, the 65816 processor also
knows JML and JSL, which are JMP and JSR using new (long) addressing
modes. ACME also accepts the new addressing modes when using the old
mnemonics JMP and JSR, but the old addressing modes cannot be used
with the new mnemonics JML and JSL.


----------------------------------------------------------------------
Section:   Argument order of MVN/MVP
----------------------------------------------------------------------

According to WDC's official syntax for 65816 assembly language, the
argument order of the MVN and MVP instructions differs between
assembly language and machine code.
To copy bytes from bank $ab to bank $cd, use the following statement:
    mvn $ab, $cd        ; source bank $ab, destination bank $cd
or
    mvn #$ab, #$cd      ; source bank $ab, destination bank $cd
ACME will then produce the following machine code:
    $54 $cd $ab ; opcode mvn, destination bank $cd, source bank $ab

ACME 0.05 and earlier did it the wrong way.


----------------------------------------------------------------------
Section:   Register lengths
----------------------------------------------------------------------

When assembling "lda #5" for example, ACME has to know whether to
create an 8-bit argument or a 16-bit argument. This depends on the
current register length.
On startup, ACME assumes all registers are 8 bits wide. You can change
this at any time using the following pseudo opcodes:

		!al	; switch to long accumulator
		!as	; switch to short accumulator
		!rl	; switch to long index registers
		!rs	; switch to short index registers

Please note that ACME, unlike some other assemblers, does *not* track
SEP/REP instructions: I don't like that method - it fails when
encountering PLPs, for example. So if it doesn't work reliably in the
first place, why use it? :)

If you don't like that you always have to use a pseudo opcode
alongside SEP/REP instructions, then have a look at the library file
<65816/std.a> which has some predefined macros you can use.


----------------------------------------------------------------------
Section:   Postfixing stuff
----------------------------------------------------------------------

You can also use the postfix method (which is explained in the file
"AddrModes.txt") to specify the immediate argument's length:

		ldx+2 #5

will always be assembled to a 16-bit argument, regardless of the
currently configured index register width. Use at your own risk - this
method obviously is not a good example on structured programming. :)


----------------------------------------------------------------------
Section:   Miscellaneous
----------------------------------------------------------------------

Note that ACME cannot produce more than 64 KBytes of code. Also note
that though the 65816 CPU has an address space of 16 MB, ACME's
program counter is only sixteen bits wide. It shouldn't be too hard to
make any assembled code run in a non-zero bank, though.