Programming the

Microprocessor

MASM

MASM (Microsoft Macro Assembler)

converts a symbolic program into a binary

program that executes on a personal

computer.

ML.EXE is the MASM program.

ML assembles a program and also links

the program.

ML uses a source file that has en

extension .asm (but any extension can be

used)

ML generates an .obj file from the source

file.

The object file is an intermediary file that is

input to a linker program (LINK.EXE).

The linker program (called by ML.EXE)

converts the .obj file into either an .exe or

.com file.

The .exe (execute) file or .com (command)

file is executed from the command prompt

by typing the name of the file.

MASM

Libraries

The LIB program creates and maintains

library files that can be linked to source

files so common functions need only be

written once.

Library files have an extension of .lib and a

special form of the library file used with

windows (dynamic library files) have an

extension .dll

Macros

Macro files are files that contain

programming steps that the assembler

inserts into a program when the macro is

invoked.

Macros have replaceable parameters that

are passed to the macro.

Macros only function in a purely assembly

language environment.

MINE MACRO A, B, C

MOV AL,A

ADD AL,B

MOV C,AL

ENDM

Use: MINE 2,3, ANSWER ;adds 2 + 3

PUBLIC and EXTRN

The PUBLIC statement makes labels

public to other programming modules.

The name of each function in a library file

or a program file can be made public.

The EXTRN (assembly language)

statement informs the assembler that a

label exists that is defined outside of the

current programming module.

Keyboard

The keyboard in Windows generates messages whenever a key is typed.

The WM_CHAR message contains the ASCII key-code.

Keyboard character are at times intercepted by a program using the PreTranslateMessage function.

PreTranslateMessage receives the message before anything else.

Filtering Keys

If a simple application using a single edit

box is created (see next slide) one can

illustrate the use of PreTranslateMessage

and filtering.

The software to filter just the numbers 0-9

is illustrated in the slide that follows the

next slide.

BOOL CssssDlg::PreTranslateMessage(MSG* pMsg)

{

if ( pMsg->message == WM_CHAR )

{

UINT key = pMsg->wParam; //get ASCII

if ( key < '0' || key > ‘9' )

return true; //ignore

}

return CDialog::PreTranslateMessage(pMsg);

}

/*This software only accepts 0 through 9, anything else is ignored. Any key or range of keys can be filtered in the same manner.*/

SetFocus

Focus is an important concept

If focus is set to an edit box or any control

that accepts keyboard data the cursor is

placed in the object.

To set focus use the SetFocus() member

function for the object.

To set focus to Edit1 (edit box) use

Edit1.SetFocus();

Obtaining Data from a Stock

Object

To obtain data from a stock control use the GetDlgItemText() or GetDlgItemInt() MFC functions.

To retrieve the text from an edit box called IDC_EDIT1 (the name assigned by Windows) use:

CString str1; GetDlgItemText(str1,IDC_EDIT1);

TO obtain an integer from an edit box called IDC_EDIT1 by the Visual Studio editor use:

int fred = GetDlgItemInt(IDC_EDIT1);

Note: The names of objects assigned by Visual Studio are in the resource file called Resource.h of each project. Also note that there is a number assigned to each name that can also be used in the Get and Set DlgItem functions as in GetDlgItemInt(101);

Placing data in a stock object

Use SetDlgItemText() or SetDlgItemInt to place data into a stock object.

For example, to place “Wow” in an edit control called IDC_EDIT1 by the framework use:

SetDlgItemText(IDC_EDIT1,”WOW”);

or

CString str1 = “WOW”;

SetDlgItemText(IDC_EDIT1,str1);

To place the number 234 into an edit control called IDC_EDIT1 use:

int numb1 = 234;

SetDlgItemInt(IDC_EDIT1,numb1);

Conversions

Converting from Hexadecimal to decimal is accomplished by subtracting 30H (0-9) from each digit or 37H (A-F) from each digit.

If AL contains a single hexadecimal digit:

SUB AL,30H

CMP AL,9

JBE LATER ;if 0-9

SUB AL,7

LATER:

Converting from to hexadecimal is accomplished by adding 30H (0-9) or adding 37H (A-F).

For example, if AL contains 0-F use:

ADD AL,30H

CMP AL,39H

JBE LATER ;if 0-9

ADD AL,7

LATER:

Example Hex to Decimal

The prior slide shows a simple application that contains a few stock labels and edit boxes. The edit boxes are IDC_EDIT1 and IDC_EDIT2 as assigned by Visual Studio.

The task is to read the number from IDC_EDIT1 (in hexadecimal) and display it (in decimal) on IDC_EDIT2.

Problem 1: We cannot read a hexadecimal number from an edit box. Only a decimal integer or a string can be read. Here we need to read a string.

Problem 2: The string needs to be converted to a decimal integer so it can be displayed on edit box 2.

CString str1;

int result = 0;

GetDlgItemText(str1,IDC_EDIT1) //get hex

for (int a = 0; a < str1.GetLength(); a++)

{

result <<=4; //shift left 4 places

char temp = str1.GetAt(a); //get digit

_asm

{

mov al,temp ;convert digit

sub al,30h

cmp al,9

jbe SOL1

sub al,7

SOL1:

mov temp,al

}

result |= temp; //put digit in result

}

SetDlgItemInt(IDC_EDIT2,result);

//in strictly C++ only

CString str1;

int result = 0;

GetDlgItemText(str1,IDC_EDIT1) //get hex

for (int a = 0; a < str1.GetLength(); a++)

{

result <<=4; //shift left 4 places

if (str1.GetAt(a) > „9‟ )

result |= str1.GetAt(a) – 0x37;

else

result |= str1.GetAt(a) – 0x30;

}

SetDlgItemInt(IDC_EDIT2,result);

Respond to the Enter Key

The enter key is 13 decimal or 0DH.

The enter key can be intercepted with the PreTranslateMessage function by trapping the WM_KEYDOWN message.

BOOL CssssDlg::PreTranslateMessage(MSG* pMsg)

{

if ( pMsg->message == WM_KEYDOWN ) //on any key down

{

if ( pMsg->wParam == 13 ) //on enter

{

//process enter key (earlier software)

return true; //we handle enter

}

}

return CDialog::PreTranslateMessage(pMsg); //framework

}

THE END