M68K2_AS(6)

NAME
m68k2_as - assembler for Motorola 68000

SYNOPSIS
~em/lib.bin/m68k2/as [options] argument ...

DESCRIPTION
This assembler is made with the general framework described in uni_ass(6). It is an assembler generating relocatable object code in ack.out(5) format.

SYNTAX

registers
    The 68000 has the following registers: seven data-registers (d1 - d7), seven address-registers (a1 - a6, sp) of which sp is the system stack pointer, a program counter (pc), a status register (sr), and a condition codes register (ccr) which is actually just the low order byte of the status register.

addressing modes
    syntax		meaning (name)
    reg		contents of reg is operand, where reg is
    		one of the registers mentioned above (register direct)
    (areg)		contents of areg is address of operand, where
    		areg is an address-register
    		(address register indirect)
    (areg)+		same as (areg), but after the address is used,
    		areg is incremented by the operand length
    		(postincrement)
    -(areg)		same as (areg), but before the address is used,
    		areg is decremented by the operand length
    		(predecrement)
    expr(areg)
    expr(pc)	expr + the contents of the register yields the
    		address of the operand (displacement)
    expr(areg, ireg)
    expr(pc, ireg)	expr + the contents of the register + the contents
    		of ireg yields the address of the operand. ireg is
    		an address- or a data-register.
    		ireg may be followed by .w or .l indicating whether
    		the size of the index is a word or a long
    		(displacement with index)
    expr		expr is the address of the operand
    		(absolute address)
    #expr		expr is the operand (immediate)
    Some instructions have as operand a register list. This list consists of one or more ranges of registers separated by '/'s. A register range consists of either one register (e.g. d3) or two registers separated by a '-' (e.g. a2-a4, or d4-d5). The two registers must be in the same set (address- or data-registers) and the first must have a lower number than the second.

instructions
    Some instructions can have a byte, word, or longword operand. This may be indicated by prepending the mnemonic with .b, .w, or .l respectively. Default is .w.

SEE ALSO
uni_ass(6), ack(1), ack.out(5),
MC68000 16-bit microprocessor User's manual, Motorola Inc, 1979

EXAMPLE

	.define	.cii

		.sect .text
	.cii:
		movem.l	a0/d0/d1,.savreg
		move.l	(sp)+,a0	! return address
		move	(sp)+,d0	! destination size
		sub	(sp)+,d0	! destination - source size
		bgt	1f
		sub	d0,sp		! pop extra bytes
		bra	3f
	1:
		move	(sp),d1
		ext.l	d1
		swap	d1
		asr	#1,d0
	2:
		move.w	d1,-(sp)
		sub	#1,d0
		bgt	2b
	3:
		move.l	a0,-(sp)
		movem.l	.savreg,a0/d0/d1
		rts