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The Commodore 64 Emulator with the extra dimension

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Commodore 64


With breakpoint actions can be triggered at given conditions.

Conditions can be logical AND which means that more then one condition has to be true within an CPU instruction to trigger the action.

Possible conditions values:

CPU.C CPU Clock Cycle
CPU.A Accumulator
CPU.X X-Register
CPU.Y Y-Register
CPU.SP Stackpointer
CPU.PC Programcounter
CPU.IRQ Interruptmask
CPU.MRD CPU Read the given data from bus
CPU.MWD CPU Write the given data from bus
CPU.MRA CPU Read access to the given address
CPU.MWA CPU Write access to the given address
CPU.F.V Overflow Flag (1=Set, 0=Cleared)
CPU.F.I  Interrupt Flag (1=Set, 0=Cleared)
CPU.F.N Negative Flag (1=Set, 0=Cleared)
CPU.F.Z Zero Flag (1=Set, 0=Cleared)
CPU.F.C Carry Flag (1=Set, 0=Cleared)
CPU.F.D Decimal Flag (1=Set, 0=Cleared)
VIC.RL Rasterline started (Use value 0 for start of frame)
VIC.IRQ VIC interrupt set mask
1541.TRACK Current Track (0... including half tracks)
1541.SYNC Sync mark (1=Sync, 0=Data)
1541.WRITE Head mode (1=Writing, 0=Reading)

Possible comparision:

= Equal
<> Not equal
> Greater
< Less
>= Greater or equal
<= Less or equal
AND Bitwise AND
MOD Modulo not equal 0
NMOD Modulo equals 0

Triggers are activated, when a condition is true or a value is not 0 (e.g. "CPU.A AND $10").

Possible actions are:

DO Executes any console command or batch file.
INFO Trace an information with the given text
WARN Trace a warning with the given text
ERROR Trace an error with the given text
BREAK Pause the system


Setting a breakpoint can be done within the Debugger or with the console command "BS"(breakpoint set).

The format is as follows:

BS <number> <condition> [condition]* [DO|INFO|WARN|ERROR|BREAK <command or text>] [ONCE] [SILENT] [DISABLE]

Using the CPU.Mxx conditions is quit tricky, because theses condition values check the read/write access to the data and address bus within the complete execution of one CPU instruction.


The following is the code of Commando, where the joystick is read from CIA:
Disassembly of Commando

We want to break execution, when any joystick contact is closed:


When you want to break, whenever a read access to the Joystick CIA port is done, just set a breakpoint as follows:


Note that this breakpoint is not bound to a specific execution address, so it will not be displayed in disassembly.