CODEWITHSUNDEEP
assemblyconditional-statementsmotorola68000
Jeremy H.
Jeremy H.

Reputation: 69

Motorola 68000 assembly comparing numbers

The program that I am in the process of writing takes input in the form of a single digit number followed by a space followed by a two digit number. The program will take the two numbers and add them together, reduce number by 7s until less than 7, and associate that number with a day of the week. Here is what I have:

start:  initIO                  * Initialize (required for I/O)
    setEVT          * Error handling routines
*   initF           * For floating point macros only       

    linein  buffer          *reads in values
    cvta2   buffer,#1       *provided macro to convert ascii to num, read first digit only
    move.b  D0,D1           *Store value in D1
    cvta2   buffer+2,#2     *read the next two digits after space
    move.b  D0,D2           *store
    add.b   D1,D2           *add them together (I can probably use just one register here)

here is the trouble:

for:    cmp.w   week, D2 *<<<<< This is saying invalid syntax, I want to see if the number provided is greater than 7, if not branch out to the next section

/trouble

    ble done
    subq.w  #7,D2        *If num>7, sub 7

done:   

    lineout dmsg

        break                   * Terminate execution
*
*----------------------------------------------------------------------
*       Storage declarations

buffer: dc.b    80
dmsg:   dc.b    'Done',0
week:   dc.b    $7    *If combined value is greater than this, sub 7
*These are the values to check against to get correct reply
sun:    dc.b    $1
mon:    dc.b    $2
tues:   dc.b    $3
weds:   dc.b    $4
thurs:  dc.b    $5
fri:    dc.b    $6
sat:    dc.b    $7
*These are the responses for the output
sunr:   dc.b    'Sunday',0
monr:   dc.b    'Monday',0
tuesr:  dc.b    'Tueday',0
wedsr:  dc.b    'Wednesday',0
thursr: dc.b    'Thursday',0
frir:   dc.b    'Friday',0
satr:   dc.b    'Saturday',0

        end

There will be more code when I figure out how to make the comparison above, but it will be the same sort of comparison just using the result against the days of the week values in order to provide the correct response.

I have tried using the various forms of cmp (cmpa, cmpi.w/l, etc), but I cannot seem to find a method that allows me to compare the two values. Would I have to load the value I labeled "week" into a register before trying to compare it or something like that?

Examples of I/O:

Input:

1 10

Output:

"Wednesday"

Any insight is appreciated. Thanks for your time.

Upvotes: 1

Views: 1911

Answers (2)

Jeremy H.
Jeremy H.

Reputation: 69

Edit(Working code for problem with the caveat that it is not optimized):

start:  initIO                  * Initialize (required for I/O)
    setEVT          * Error handling routines
*   initF           * For floating point macros only    

    linein  buffer
    cvta2   buffer,#1   
    move.l  D0,D1
    cvta2   buffer+2,#2
    move.l  D0,D2
    add.l   D1,D2    

    divu.w  #$0007,D2   

    lsr.l   #$08,D2 *Shift remainder
    lsr.l   #$08,D2    

    move.w  sun,A2
    cmp.w   A2,D2
    BNE monday
    lineout sunr
    BEQ end

monday: 
    move.w  mon,A2
    cmp.w   A2,D2
    BNE tuesda
    lineout monr
    BEQ end    

tuesda: 
    move.w  tues,A2
    cmp.w   A2,D2
    BNE wednes
    lineout tuesr
    BEQ end    

wednes: 
    move.w  weds,A2
    cmp.w   A2,D2
    BNE thursd
    lineout wedsr
    BEQ end    

thursd: 
    move.w  thurs,A2
    cmp.w   A2,D2
    BNE friday
    lineout thursr
    BEQ end    

friday: 
    move.w  fri,A2
    cmp.w   A2,D2
    BNE saturd
    lineout frir
    BEQ end    

saturd: 
    lineout satr
    BEQ end    

end:    
        break                   * Terminate execution
*
*----------------------------------------------------------------------
*       Storage declarations

buffer: dc.b    80
wkmsg:  dc.w    'The day of the week is '
week:   equ $7
sun:    dc.w    $1
mon:    dc.w    $2
tues:   dc.w    $3
weds:   dc.w    $4
thurs:  dc.w    $5
fri:    dc.w    $6
sat:    dc.w    $7
sunr:   dc.w    'Sunday',0
monr:   dc.w    'Monday',0
tuesr:  dc.w    'Tueday',0
wedsr:  dc.w    'Wednesday',0
thursr: dc.w    'Thursday',0
frir:   dc.w    'Friday',0
satr:   dc.w    'Saturday',0

        end

Upvotes: 0

MutenFuzz
MutenFuzz

Reputation: 135

You are trying to perform a comparison with an unsupported addressing mode (in your example the 'week' operand is not an immediate value, but a memory address).

To compare D2 with 7 you can use cmpi (compare immediate):

cmpi.b #7,d2

In case you need the operand to be a variable, you must load it into a register first:

lea week,a0
...
cmp.b (a0),d2

Also make sure the operand size in the cmp instruction matches the size of your data

Upvotes: 1

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