Use simtower dosbox
- #Use simtower dosbox how to
- #Use simtower dosbox install
- #Use simtower dosbox code
- #Use simtower dosbox download
Determines if the index values should be increased or decreased when executing a string operation. Direction Flag – Used for direction when moving or comparing string data.Parity Flag – Shows if the number of 1-bits in the result of an arithmetic operation is even or odd.Auxiliary Carry Flag – Works as the Carry Flag, but treats all bytes as BCD numbers (minus the shift and rotate part).Overflow Flag – Works as the Carry Flag, but treat all bytes as Two’s complement signed numbers (minus the shift and rotate part).It basically tells if the highest bit of the result is set to 1 or 0. Sign Flag – Shows if the result of an operation might be Two’s complement signed or not (that it might represent a negative number).A non-zero or non-equal result set flag to 0. Zero Flag – Is set to 1 when the result of an arithmetic operation is zero or when two compared values are equal.
It will also store the bit that is removed doing a shift or rotate operation.
#Use simtower dosbox code
In DOSBox the pairing a segment and register will look like DS:SI, CS:IP, SS:SP etc in the Code overview.Īfter all the registers and segments, we have the Flags. Because they can overlap, different looking segment + offset combinations can point to the same physical address. Hexadecimal:ĭifferent segments can overlap and even point to exact same region. You get the physical addresses from a segment and pointer by multiply the segment with 16 and then adding the pointer value to it.įor example if DS is 0x2052 and SI is 0x05BC, the physical address will be 0x20ADC. Together with a register in the second column they can point to a specific address in the memory. FS and GS can be referred to as Far segment and Global segment respectively, but there is no difference between them. Their value is an address in the physical memory divided by 16. Each define a 64 Kb large region of memory space. Meaning that if EAX is set to 0xFFDD9900, AX is 0x9900, AH is 0x99 and AL is 0x00.Īfter the two columns we find a bunch of Segment registers. EAX will access all 4 bytes (32-bits), AX will access the two lower bytes (16-bits), AH will access the higher byte of AX and AL will access the lower byte of AX. For example the bytes in the Accumulator can be referenced by EAX, AX, AH and AL. The bytes in the GPs can be referenced in code by four different ways. In the first column we have the four general purpose registers (Accumulator, Base, Count and Data) and their current 32-bit value. In the above screen shot you can see that EIP was changed. Registers and flags that were changed by the previous executed instruction will be highlighted. Meaning that the most significant byte is shown first. The registers represent “memory slots” in the emulated CPU.Īll values shown are displayed in big endian fashion. It shows all the registers, flags and their current values (There is also some other stuff on the right side I haven’t 100% figured out yet). Register Overviewįirst section of the screen is the Register Overview. Almost all numbers are shown in hexadecimal. In the text below I assume you are familiar with bits, bytes and hexadecimal formatting. The commands are also listed on this page. When the execution is stopped, you can type “help” in the debug screen to see additional commands to use. Or if you want to start debugging immediately, start the application by typing “debug” before the name of the executable. You can start an application as normal and then press Alt+Break and F5 to stop/start the execution of code.
#Use simtower dosbox download
If you already have DOSBox installed, you’ll only need to download the EXE-file and add it to the folder where regular DOSBox is installed.ĭOSBox Debugger will start as the normal version of DOSBox, but with the additional debug screen showing.
#Use simtower dosbox install
How the get the Debug screenįirstly, to even see this screen in DOSBox, You’ll need to install a special debug version if it. So I have, in order to make myself understand it better and to make it easy for anyone else who want to follow my footsteps, decided to write this overview of the screen and its parts. And when being new to both, the debug screen in DOSBox is a bit overwhelming.
#Use simtower dosbox how to
I have recently begun the journey of learning to code old DOS assembly and how to debug it in the debug version of DOSBox.