Altair 680

[mon...@gmail.com]

Hello All,

I received and built the Altair 680, a fun project and would recommend to anyone who enjoys building kits.

My question since I am not a programmer is:

How do you Add Two Numbers in Altair 680 Machine Code

I tried the following code I found on the internet.  Some things do not make sense to me

Address Opcode Instruction Comments
0x00 0xA9 LDA #$05 Load the first number (5)
0x01 0x05
0x02 0xA2 LDX #$03 Load the second number (3)
0x03 0x03
0x04 0x86 ADD A, X Add the two numbers
0x05 0x00
0x06 0x00 STAA $FF Store the result at address $FF

Then hit RUN and then checked location FF - no luck

Any help would be greatly appreciated.

Thanks,

Maurice

[Tom Lake]

Don't you need a HLT or RTN at the end? How does the code know when to stop trying to execute instructions?

[Chris Davis]

It looks like this is 6502 code.  For example, LDA on a 6502 is 0xA9, but LDAA on a 6800 is 0x86.

Here's a version of that code for 6800:

        0x0000  0x86  LDAA  #$05     ; A = 5

        0x0001  0x05
        0x0002  0xC6  LDAB  #$03     ; B = 3

        0x0003  0x03
        0x0004  0x1B  ABA            ; A = A + B

        0x0005  0x97  STAA  $FF      ; store result at $00FF

        0x0006  0xFF

The final bytes are 86 05 C6 03 1B 97 FF

I have not tested this, but it should work.

[Kelly Loyd]

The code works. I like to put an SWI at the end - seems to work universally between SWTPC and Altair680 and return me to the Monitor.

   0000                         org $0000
   0000   86 05         Start   ldaa #$05
   0002   c6 03                 ldab #$03
   0004   1b                    aba
   0005   97 ff                 staa $ff
   0007   3f                    SWI

Used the Altair Mon L command to transfer the S-record file

.J 0000
.M 00FF 08 

[Maurice Onraet]

Hello Kelly,

Thanks so much for your help.

Much appreciated.....

Kindly,

Maurice

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