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<!doctype HTML public "-//W3O//DTD W3 HTML 3.0//EN"><HTML><HEAD><TITLE>8086 Assembler Tutorial for Beginners (Part 5)</TITLE><META name="description" content="Library of common functions - emu8086.inc"><META name="keywords" content="common functions, emu8086.inc, 8086, tutorial, programming, assembler tutorial, tutorial for begginers"><META name="robots" content="nofollow"></HEAD><BODY bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#007099" alink="#FF0000"><FONT FACE="Verdana" SIZE=3><TABLE WIDTH=80%><TR><TD><FONT SIZE=+1><B>8086 Assembler Tutorial for Beginners (Part 5)</B></FONT><BR><BR><FONT SIZE=+2><B>Library of common functions - emu8086.inc</B></FONT><BR><BR>To make programming easier there are some common functions that canbe included in your program. To make your program use functions definedin other file you should use the <B>INCLUDE</B> directive followed bya file name. Compiler automatically searches for the file in the samefolder where the source file is located, and if it cannot find the filethere - it searches in <B>Inc</B> folder.<BR><BR>Currently you may not be able to fully understand the contents of the <B>emu8086.inc</B>(located in <B>Inc</B> folder), but it's OK, since you only need to understandwhat it can do.<BR><BR>To use any of the functions in <B>emu8086.inc</B> you should have the following linein the beginning of your source file:<BR><BR><FONT FACE="Fixedsys">include 'emu8086.inc'</FONT><BR><BR><HR><BR><B>emu8086.inc</B> defines the following <B>macros</B>:<BR><BR><UL><LI><B>PUTC char</B> - macro with 1 parameter, prints out an ASCII char at current cursor position.<BR><BR></LI><LI><B>GOTOXY col, row</B> - macro with 2 parameters, sets cursor position.<BR><BR></LI><LI><B>PRINT string</B> - macro with 1 parameter, prints out a string.<BR><BR></LI><LI><B>PRINTN string</B> - macro with 1 parameter, prints out a string. The same as PRINT but automatically adds "carriage return" at the end of the string.<BR><BR></LI><LI><B>CURSOROFF</B> - turns off the text cursor.<BR><BR></LI><LI><B>CURSORON</B> - turns on the text cursor.<BR><BR></LI></UL>To use any of the above macros simply type its name somewhere in your code,and if required parameters, for example:<BR><BR><TABLE BORDER=1 CELLPADDING=10 WIDTH=50%><TR><TD><PRE><FONT FACE="Fixedsys">include emu8086.incORG 100hPRINT 'Hello World!'GOTOXY 10, 5PUTC 65 ; 65 - is an ASCII code for 'A'PUTC 'B'RET ; return to operating system.END ; directive to stop the compiler.</FONT></PRE></TD></TR></TABLE><BR><BR>When compiler process your source code it searches the <B>emu8086.inc</B> filefor declarations of the macros and replaces the macro names with real code.Generally macros are relatively small parts of code, frequentuse of a macro may make your executable too big (procedures are betterfor size optimization).<BR><BR><HR><BR><B>emu8086.inc</B> also defines the following <B>procedures</B>:<BR><BR><UL><LI><B>PRINT_STRING</B> - procedure to print a null terminated string at current cursor position, receives address of string in <B>DS:SI</B> register. To use it declare: <B>DEFINE_PRINT_STRING</B> before <B>END</B> directive.<BR><BR></LI><LI><B>PTHIS</B> - procedure to print a null terminated string at current cursor position (just as PRINT_STRING), but receives address of string from Stack. The ZERO TERMINATED string should be defined just after the CALL instruction. For example:<BR><BR> <FONT FACE="Fixedsys"> CALL PTHIS<BR> db 'Hello World!', 0<BR><BR> </FONT> To use it declare: <B>DEFINE_PTHIS</B> before <B>END</B> directive.<BR><BR></LI><LI><B>GET_STRING</B> - procedure to get a null terminatedstring from a user, the received string is written to bufferat <B>DS:DI</B>, buffer size should be in <B>DX</B>.Procedure stops the input when 'Enter' is pressed. To use it declare: <B>DEFINE_GET_STRING</B> before <B>END</B> directive.<BR><BR></LI><LI><B>CLEAR_SCREEN</B> - procedure to clear the screen,(done by scrolling entire screen window),and set cursor position to top of it. To use it declare: <B>DEFINE_CLEAR_SCREEN</B> before <B>END</B> directive.<BR><BR></LI><LI><B>SCAN_NUM</B> - procedure that gets the multi-digit SIGNED number from the keyboard, and stores the result in <B>CX</B> register. To use it declare: <B>DEFINE_SCAN_NUM</B> before <B>END</B> directive.<BR><BR></LI><LI><B>PRINT_NUM</B> - procedure that prints a signed number in <B>AX</B> register.To use it declare: <B>DEFINE_PRINT_NUM</B> <U>and</U> <B>DEFINE_PRINT_NUM_UNS</B> before <B>END</B> directive.<BR><BR></LI><LI><B>PRINT_NUM_UNS</B> - procedure that prints out an unsignednumber in <B>AX</B> register. To use it declare: <B>DEFINE_PRINT_NUM_UNS</B> before <B>END</B> directive.<BR><BR></LI></UL><BR>To use any of the above procedures you should first declare thefunction in the bottom of your file (but before <B>END</B>!!), and thenuse <B>CALL</B> instruction followed by a procedure name.For example:<BR><BR><TABLE BORDER=1 CELLPADDING=10 WIDTH=50%><TR><TD><PRE><FONT FACE="Fixedsys">include 'emu8086.inc'ORG 100hLEA SI, msg1 ; ask for the numberCALL print_string ;CALL scan_num ; get number in CX.MOV AX, CX ; copy the number to AX.; print the following string:CALL pthisDB 13, 10, 'You have entered: ', 0CALL print_num ; print number in AX.RET ; return to operating system.msg1 DB 'Enter the number: ', 0DEFINE_SCAN_NUMDEFINE_PRINT_STRINGDEFINE_PRINT_NUMDEFINE_PRINT_NUM_UNS ; required for print_num.DEFINE_PTHISEND ; directive to stop the compiler.</FONT></PRE></TD></TR></TABLE><BR><BR>First compiler processes the declarations (these are just regular the macrosthat are expanded to procedures). When compiler gets to <B>CALL</B>instruction it replaces the procedure name with the address of the codewhere the procedure is declared. When <B>CALL</B> instruction is executed controlis transferred to procedure. This is quite useful, since even if youcall the same procedure 100 times in your code you will still have relativelysmall executable size. Seems complicated, isn't it? That's ok, with thetime you will learn more, currently it's required that you understand thebasic principle.<BR><BR><BR><HR><CENTER><A HREF="asm_tutorial_04.html"><B> <<< Previous Part <<< </B></A> <A HREF="asm_tutorial_06.html"><B> >>> Next Part >>> </B></A></CENTER><HR></TD></TR></TABLE><BR></FONT></BODY></HTML>⌨️ 快捷键说明
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