Assembly language provides two instructions for stack operations: PUSH and POP. These instructions have syntaxes like − PUSH operand POP address/.

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Procedures or subroutines are very important in assembly language, as the assembly language programs tend to be large in size. Procedures are identified by a name. Following this name, the body of the procedure is described which performs a well-defined job. End of the procedure is indicated by a return statement.

Syntax

Following is the syntax to define a procedure −

The procedure is called from another function by using the CALL instruction. The CALL instruction should have the name of the called procedure as an argument as shown below −

The called procedure returns the control to the calling procedure by using the RET instruction.

Example

Pro evolution soccer 2015 full version crack download. Let us write a very simple procedure named sum that adds the variables stored in the ECX and EDX register and returns the sum in the EAX register −

When the above code is compiled and executed, it produces the following result − Pitfall lost expedition.

Stacks Data Structure

A stack is an array-like data structure in the memory in which data can be stored and removed from a location called the 'top' of the stack. The data that needs to be stored is 'pushed' into the stack and data to be retrieved is 'popped' out from the stack. Stack is a LIFO data structure, i.e., the data stored first is retrieved last.

Assembly language provides two instructions for stack operations: PUSH and POP. These instructions have syntaxes like −

The memory space reserved in the stack segment is used for implementing stack. The registers SS and ESP (or SP) are used for implementing the stack. The top of the stack, which points to the last data item inserted into the stack is pointed to by the SS:ESP register, where the SS register points to the beginning of the stack segment and the SP (or ESP) gives the offset into the stack segment.

The stack implementation has the following characteristics −

• Only words or doublewords could be saved into the stack, not a byte.

• The stack grows in the reverse direction, i.e., toward the lower memory address

• The top of the stack points to the last item inserted in the stack; it points to the lower byte of the last word inserted.

As we discussed about storing the values of the registers in the stack before using them for some use; it can be done in following way −

Example

The following program displays the entire ASCII character set. The main program calls a procedure named display, which displays the ASCII character set.

When the above code is compiled and executed, it produces the following result −

Hi,Could you please let me know the meaning of using PUSH and Pop instructions in the following program.1. Why are they necessarily required in functions Getc and Putc2. In function Getc why Push AX and Pop AX is not coded and while thesame is coded in PutcAny help would be appreciated.Below is the code for your reference.; program to get a character from a keyboard and then print to the screen; Assembler: Tasm; Operating system: MS-DOS 6. 2; compilation: Tasm test.asm; linking: tlink test.obj; execution: test.exe.Model Small.Stack 100H.CodeStart:Call GetcCall PutcCall ExitGetc:; gets a character from user; this routine gets a character into the AX registerPush BXPush CXPush DXMov AH, 01HInt 21HPop DXPop CXPop BXRetPutc:; prints a character to the screenPush AXPush BXPush CXPush DXMov DL, ALMov AH, 02HInt 21HPop DXPop CXPop BXPop AXRetExit:Mov AH, 4CHInt 21HEnd Start.

PUSH saves a register to the stack, POP restores it.The routines you show save the external registers because they need to use them for their own purposes, and do not want to corrupt the registers for the calling program. If they didn't do it, then the calling program would have to do it before and after each call, which is both inefficient, and dangerous - if you forget for just one instance of the call, you will get corrupted registers, and your program will not work.It is pretty normal for a routine to save it's working registers in this way.editI lost a letter! - OriginalGriff/edit. When answering a question please:.

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