To make a program in assembler two choices exist, the earliest one is to use the TASM or Turbo Assembler, of Borland, and the next one is to use the debugger, generally we use this last one since it is found in any PC with the MS-DOS, which creates it available to any user who has access to a machine with these features.
Debug can only make files with a .COM extension, and because of the features of these kinds of programs they cannot be larger than 64 kb, and they also must begin with displacement, offset, or 0100H memory direction within the specific segment.
Debug gives a set of commands that lets you perform a number of helpful
operations:
A Assemble symbolic instructions into machine code
D Display the contents of an area of memory
E Enter data into memory, beginning at a specific location
R Display the contents of one or more registers
G Run the executable program in memory
N Name a program
P Proceed, or execute a set of related instructions
Q Quit the debug program
T Trace the contents of one instruction
U Unassembled machine code into symbolic code
W Write a program onto disk
It is achievable to visualize the values of the internal registers of the CPU using the Debug program. To start working with Debug, kind the following prompt in your computer:
C :/> Debug [Enter]
On the next line a dash will come out, this is the indicator of Debug, at this instant the instructions of Debug can be introduced using command as follows:
-r [Enter]
AX=0000 BX=0000 CX=0000 DX=0000 SP=FFEE BP=0000 SI=0000 DI=0000
DS=0D62 ES=0D62 SS=0D62 CS=0D62 IP=0100 NV EI PL NZ NA PO NC
0D62:0100 2E CS:
0D62:0101 803ED3DF00 CMP BYTE PTR [DFD3],00 CS:DFD3=03
The complete content of the internal registers of the CPU are displayed; an
alternative of viewing them is to use the "r" command by means of as a parameter
the name of the register whose value wants to be seen. for instance:
-rbx
BX 0000
:
This instruction will only display the content of the BX register and the Debug indicator changes from "-" to ":"