MICRO
UNIT - 5Programming – 3 Q1) write a program to display 74 on screen?A1) // place at top of program // will not function in 64-bit mode void ConvertAam(char number, char* data) {_asm{mov ebx,data ;pointer to ebxmov al,number ;get test datamov ah,0 ;clear AHaam ;convert to BCDadd ah,20hcmp al,20h ;test for leading zeroje D1 ;if leading zeroadd ah,10h ;convert to ASCIID1:mov [ebx], ahadd al,30h ;convert to ASCIImov [ebx+1], al}}private: System::Void Form1_Load(System::Objectˆ sender,System::EventArgsˆ e){char temp[2]; // place for resultConvertAam(74, temp);Char a = temp[0];Char b = temp[1];label1->Text = Convert: :ToString(a) + Convert::ToString(b);} Q2) WAP to convert 32-bit unsigned number to ASCII and display on video screen?A2) void Converts(int number, int radix, char* data) {_asm{mov ebx,data ;initialize pointerpush radixmov eax, number ;get test dataL1:mov edx,0 ;clear edxdiv radix ;divide by basepush edx ;save remaindercmp eax,0jnz L1 ;repeat until 0L2:pop edx ;get remaindercmp edx,radixje L4 ;if finishedadd dl,30h ;convert to ASCIIcmp dl,39hjbe L3add dl,7 L3:mov [ebx],dl ;save digitinc ebx ;point to nextjmp l2 ;repeat until doneL4:mov byte ptr[ebx],0 ;save null in string}}private: System::Void Form1_Load(System::Objectˆ sender,System::EventArgsˆ e){char temp[32]; // place for resultConverts(7423, 10, temp);Stringˆ a = “”;int count = 0;while (temp[count] != 0) // convert to string{Char b = temp[count++];a += b;}label1->Text = a;} Q3) WAP to convert from ASCII to binary?A3) int ConvertAscii(char* data) {int number = 0;_asm{mov ebx,data ;intialize pointermov ecx,0B1:mov cl,[ebx] ;get digitinc ebx ;address next digitcmp cl,0 ;if null foundje B2sub cl,30h ;convert from ASCII to BCDmov eax,10 ;x10mul numberadd eax,ecx ;add digitmov number,eax ;save resultjmp B1B2:}return number;}private: System::Void Form1_Load(System::Objectˆ sender,System::EventArgsˆ e){char temp[] = “2316”; // stringint number = ConvertAscii(temp);label1->Text = Convert::ToString(number);} Q4) Define Macro and explain with example?A4) A macro is a group of instructions that perform one task, just as a procedure performs one task. The difference is that a procedure is accessed via a CALL instruction, whereas a macro, and all the instructions defined in the macro, is inserted in the program at the point of usage. Creating a macro is very similar to creating a new opcode, which is actually a sequence of instructions, in this case, that can be used in the program. Example below shows how a macro is created and used in a program. The first six lines of code define the macro. This macro moves the word-sized contents of memory location B into word-sized memory location A. After the macro is defined in the example, it is used twice. The macro is expanded by the assembler in this example, so that you can see how it assembles to generate the moves. Any hexadecimal machine language statement followed by a number (1, in this example) is a macro expansion statement.EXAMPLE
Q5) Explain PUBLIC and EXTERN using an example?A5) The PUBLIC and EXTRN directives are very important to modular programming because they allow communications between modules. We use PUBLIC to declare that labels of code, data, or entire segments are available to other program modules. EXTRN (external) declares that labels are external to a module. Without these statements, modules could not be linked together to create a program by using modular programming techniques. They might link, but one module would not be able to communicate to another. The PUBLIC directive is placed in the opcode field of an assembly language statement to define a label as public, so that the label can be used (seen by) by other modules. The label declared as public can be a jump address, a data address, or an entire segment. Example below shows the PUBLIC statement used to define some labels and make them public to other modules in a program fragment. When segments are made public, they are combined with other public segments that contain data with the same segment name. EXAMPLE model flat, c.datapublic Data1 ;declare Data1 and Data2 publicpublic Data20000 0064[ 00 ] Data1 db 100 dup(?)0064 0064[00] Data2 db 100 dup(?) 00 ].code.startuppublic Read ; declare Read public0006 B4 06 Read proc far mov ah,6The EXTRN statement appears in both data and code segments to define labels as external to the segment. If data are defined as external, their sizes must be defined as BYTE, WORD, or DWORD. If a jump or call address is external, it must be defined as NEAR or FAR. Q6) How C function can be used in assembly procedure explain with an example?A6) In most cases, calling C library routines or functions from an assembly program is more complex than calling assembly programs from C. An example of how to call the printflibrary function from within an assembly program is shown next, followed by comments on how it actually works. global _mainextern _printfsection .datatext db "291 is the best!", 10, 0strformat db "%s", 0section .code_mainpush dword textpush dword strformatcall _printfadd esp, 8retNotice that the procedure is declared global, and its name must be _main, which is the starting point of all C code. Since C pushes its arguments onto the stack in reverse order, the offset of the string is pushed first, followed by the offset of the format string. The C function can then be called, but care must be taken to restore the stack once it has completed. When linking the assembly code, include the standard C library (or the library containing the functions you use) in the link. For a more detailed (and perhaps more accurate) description of the procedures involved in calling C functions, refer to another text on the subject. Q7) How can we allocate local data space on stack explain?A7) Temporary storage space for local variables or data can be created by decreasing the contents of ESP just after setting up a stack frame at the beginning of the procedure. It is important to restore the stack space at the end of the procedure. The following code fragment illustrates the basic idea: push ebp ; Save caller's stack framemov ebp, esp ; Establish new stack frame sub esp, 4 ; Allocate local data space of ; 4 bytes push esi ; Save critical registers push edi. pop edi ; Restore critical registerspop esi mov esp, ebp ; Restore the stack pop ebp ; Restore the frameret Q8) How a value is returned from procedure?A8) Assembly can return values to the C calling program using only the EAX register. If the returned value is only four bytes or less, the result is returned in register EAX. If the item is larger than four bytes, a pointer is returned in EAX which points to the item. Here is a short table of the C variable types and how they are returned by the assembly code: Data Type Registerchar ALshort AXint, long, pointer EAX(*) Q9) Why it is necessary to setup a stack frame when entering a procedure?A9) Whenever entering a procedure, it is necessary to set up a stack frame on which to pass parameters. Of course, if the procedure doesn't use the stack, then it is not necessary. To accomplish the stack setup, include the following code in the procedure: push ebp mov ebp, esp EBP allows us to use this pointer as an index into the stack, and should not be altered throughout the procedure unless caution is taken. Each parameter passed to the procedure can now be accessed as an offset from EBP. This is commonly known as a standard stack frame. Q10) Explain need of combining assembly language with C/C++?A10) Often it is a good idea to link assembly language programs or routines with high-level programs which may contain resources unavailable to you through direct assembly programming--such as using C's built-in graphics library functions or string-processing functions. Conversely, it is often necessary to include short assembly routines in a compiled high-level program to take advantage of the speed of machine language. All high-level languages have specific calling conventions which allow one language to communicate to the other; i.e., to send variables, values, etc. The assembly-language program that is written in conjunction with the high-level language must also reflect these conventions if the two are to be successfully integrated. Usually, high-level languages pass parameters to subroutines by utilizing the stack. This is also the case for C.
MOVE MACRO A,B PUSH AX MOV AX,B MOV A,AX POP AX ENDM MOVE VAR1,VAR2 ;;move VAR2 into VAR1 0000 50 1 PUSH AX 0001 A1 0002 R 1 MOV AX,VAR2 0004 A3 0000 R 1 MOV VAR1,AX 0007 58 1 POP AX MOVE VAR3,VAR4 ;;move VAR4 into VAR3 0008 50 1 PUSH AX 0009 A1 0006 R 1 MOV AX,VAR4 000C A3 0004 R 1 MOV VAR3,AX 000F 58 1 POP AX
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