About
=====

dis8080 is an Intel 8080 instruction disassembler. It reads machine
code from standard input and writes the disassembly to standard
output.


Usage
=====

    dis8080 [-d ADDR COUNT]

The option -d ADDR COUNT tells the disassembler to emit data
definitions instead of instructions for COUNT bytes, starting at
input offset ADDR. This option can be used multiple times.

Output from dis8080 can be assembled with an assembler such as vasm
or asmx.


Build
=====

Compile dis8080 with an ANSI C compiler:

    cc dis8080.c -o dis8080


Examples
========

To disassemble the file example/add.bin, issue:

    ./dis8080 < example/add.bin

It generates the following output.

-----------------------------------------------------
                lxi     b,L0009
                lxi     h,L000A
                jmp     L000B
        L0009:
                mov     d,d
        L000A:
                call    L860A
                ret

        L000B   = $000B
        L860A   = $860A

        end
-----------------------------------------------------

This does not look quite right, because:
* The two "lxi" instructions hint that the values at label L0009
  and L000A should be interpreted as data rather than instructions.
* "jmp" is unconditional so the "mov" will not be executed.
* The "jmp" target is inside the "call" instruction.
* "mov d,d" is not a commonly used instruction.

What is happening here is that the disassembler does not know that
following the "jmp" are two bytes of data, after which the program
instruction stream continues at address $000B. In other words, the
disassembler has become "out of phase". It is common to encounter
cases like this in production code.

To get a more realistic disassembly, mark the addresses $0009 and
$000A as data with the -d option:

    ./dis8080 < example/add.bin -d 0x0009 2

-----------------------------------------------------
                lxi     b,L0009
                lxi     h,L000A
                jmp     L000B
        L0009:
                db      $52             ; 'R'
        L000A:
                db      $cd
        L000B:
                ldax    b
                add     m
                ret


        end
-----------------------------------------------------

Now this looks better as locations $0009 and $000A are interpreted
as data rather than instructions. At label L000B the two data bytes
in memory are added together.