* file = example0.asm
* Quick examples of Assembler directives & 6812 code
* Dr. Karl Gugel, 12/2001
* Dr. Eric Schwartz 21May2002

* Sim12 is based on the M68HC12AEVB. It assumes the following memory map:
* 16K External RAM at $4000-$7FFF
* 32K External ROM at $8000-$FFFF
* Internal RAM at $800-$BFF
* Internal EEPROM at $1000-$1FFF
* Note: You can load in programs anywhere in the above mentioned areas but should
*       only write to RAM (i.e. assume ROM and EEPROM are read only).  

* Assemble using the "MiniIDE" 6812 Assembler found on our web site.
* Inside of MiniIDE go to "Build" => "Options" and make sure the "Generate Listing 
* File" option is checked.
**************************************************************

* ASSEMBLER EQUATE (Define) Statements
CONST	EQU	$8000	;starting address for constants in memory
RAM1	EQU	$4000	;starting address for variables in memory
RAM2	EQU	$5000	;starting address for additional variables in memory

* DATA ALLOCATION SECTION - constants & variables
* Data can go before or after your program but should
* not in the middle of a program for clarity reasons.
        org     CONST	;these are all assembler directives
num1    dc.b    $CD  	;define byter, single byte placed in memory starting at $1000     
num2    dc.w    $1234	;define word, double byte placed in memory
char    dc.b    'E' 	;define string, ASCII characters (one byte each)
        dc.b    'E'
        dc.b    'L'
        dc.b    '4'
        dc.b    '7'
        dc.b    '4'
        dc.b    '4'

	org	RAM1	
results ds.b    3	;locations $4000-$4002 reserved for future use

        org     RAM2
value1  dc.b    27      ;put 27 decimal in mem @ $5000
value2  dc.b    30      ;put 30 decimal in mem @ $5001
sum	ds.b	1	;reserve a byte for a future sum

* Special Note:  Assembler directives are used to place data
*                and variables into memory.  They are not 6811
*                instructions and thus are not executed at run
*                time.  When this program is loaded into memory,
*                the data (created above by the assembler) is also
*                copied down into memory.



* Data Transfer Examples
* Program #1 - moving a byte to a new location

        org     $1000   ;we will fill in comments in class
        ldaa    num1   	;
        staa    results ;
end1	bra	end1

* Program #2 - moving a word (two bytes) to a new location
	org	$1100
	ldd	num2	;
        std     results ;
end2	bra	end2

* Program #3 - load immediate data, transfer to another register & store in mem
	org	$1200
	ldaa	#%10101110	;
	tab			;
	stab	results		;
end3	bra	end3

* Program #4 - move data using an index register
	org	$1300
	ldx	#num1		;
	ldy	#results	;
	ldaa	0,x		;
        staa    2,y             ;
end4	bra	end4

* ARITHMETIC & LOGIC EXAMPLES
* Program #5 - adding (2) byte size numbers & saving the result
        org     $1400
        ldaa    value1		;
	ldab	value2		;
	aba			;
        staa    sum             
end5	bra	end5

* Program #6 - subtracting a byte in memory from an immedate data byte
	org	$1500
	ldab	#$20		;
	subb	value2		;
        ldx     #sum            ;
        stab    0,x             
end6	bra	end6

* Program #7 - summing words
	org	$1600
	ldd	num2		;
	addd	num2		;
	ldy	#results	;
        std     9,y             ;
end7	bra	end7

* Program #8 - bit wise ANDing example
	org	$1700
	ldaa	num1
	nega			;
	anda 	value1		;
        staa    sum             
end8	bra	end8