MOV AH,9 INT 21H I think you have got this idea. MOV AH, 2 INT 21H Again if we put value 9 in AH register and call an interrupt it will print the string as output. We will discuss about the output later. Again if we put value 2 in AH register and call an interrupt and it will print single character as output.
Print Register Value Emu8086 Code Ive Ever
Would not it be easy to make a variable indicate this memory address?Contribute to AhmadNaserTurnkeySolutions/emu8086 development by creating an account on GitHub. We wrote the data at "0b800h:0h" in the previous article. So the assembler and compiler allows you to use variables. But the address of the memory is a number and the number is hard for us to remember. Emu8086.The variable is just the address of the memory. In fact the most genius assembly code ive ever seen.
Printf AX doesn't work and i want to print the contents of AX. And simpler function to print out binary value of AL register. The recursive function to print decimal UNsigned value of AL register.
I mentioned that the variable is the address of the memory. But there is something more important here. "DW" declares a word size variable.If you run the program with the emulator, you can see that the AL and BX values change to h, respectively.Simple. It declares a variable with one byte size. "DB" can be read as define byte or data byte.
I mentioned that the address of memory is in. You can see after the ret command.And on the right side of the emulator screen, it looks like mov al. When the ret command is executed, the program is finished. The C3 value is stored in memory address 7107h. If you see h somewhere in the emulator, that's the location of the variables we created.The number corresponding to the ret command (AKA, machine code) is C3. The values of the variables we created are h.
We have declared the variables immediately after the ret command, which is stored immediately after the ret command in the actual program.The strange thing is that it looks like 3412 while we saved 1234h. Is it 07?There are the variables we declared. Check the value of address 7108h. Since the value of ds is 700h, the final address value is 7108h. But you should always think of segment registers when calculating the address. You might forget ds and think of the address as 108h.
There are various reasons, but for the details, please refer to Wikipedia.When we declare a variable between source code, will the program have that variable in place? Let's try following code. Since the unit of memory is a byte, it is not stored as 87654321, but it is divided into bytes and its order is changed byte by byte. When 16 bits 1234h is written, 34, 12 are stored in the order, and when 32 bits 12345678h are stored, 78, 56, 34, 12 are stored. Little endian is to store the values written to memory in reverse order by the program. Conversely, there is a big endian. It is not a little Indian -), but an endian.
According to the little endian convention, the numbers we should find are 20, 01. What is the memory address the addr located at? Find the value 120h. Why? As I said above, this is because the variable is a memory location. The mov word ptr , 1234h command assembled into mov word ptr , 1234h as we wrote? No, that's why I asked.Looking at the assembled code, it appears as mov word ptr , 1234h. That is, we want to store the value 1234h in the ds: address. If you pass the number 103h to the address value, processor will read the memory at 103h and bring it into the register.So what happens if the variable value itself is an address value? So how can we mimic a pointer variable? ORG 100hIf you look at the source, you have the addr variable that is 120h.
However, mov al, var1 is a translation that the assembler provides for human readability, and the syntax understood by the original machine is mov al, byte ptr. Mov al, var1 looks like it would pass the value in var1 into al directly, but in fact it is calculating the memory address of var1 and then reading the data from that address in memory and store the data in the register.The equality of mov al, var1 and mov al, byte ptr may seem strange. Think of variables as memory locations.
And then you can access memory using the register values.Normal variables are accessed at once because we know the address of the variable and read the memory once. Why is it indirect? To access the address value stored in the pointer variable, as we did in the assembly language, you must first read the address value stored in the variable into the register. A value of 34 12 will appear.In C, writing a value into a memory addressed by a pointer variable is called indirect reference. Finally, we store a value of 1234h in the ds: location.Press the aux button on the emulator to open the memory window and check the memory at address 0700:1234. And when mov bx, addr command is executed, 1234h value is stored in bx register.
There is one more memory access so that it's called as indirect reference.Note1: unsigned short *p = 0xb8000 this is a way to store the address value in the variable.
0 kommentar(er)
