Conventionally constructing and downloading program code(s) for microcontroller(s) must be done throughout there steps: designing and constructing assembly program (codes), compiling the assembly program, and dowloading program codes to microcontroller as a target. Naturally the three steps above uses different application program that felt as not effective and efficient. So that it must be a way to make it simpler in nature. The application software constructed here is as an alternative solution to solve inffective and inefficient that conventional procedures, because in this constructed software of application: editor, compiler and programmer had been integrated in a such manner. Each function of these aspects is: editor works as to make an assembly program, compiler works as to compile any program designed and programmer as it called used to dowload the program codes to related of microcontroller. There are additional facilities needed for this application software, namely: (1) code generator, the function of this software is to make some simple codes of program for LED programming, 7 segments, input from the switch and time delay needed; (2) terminal, used as communication media between the computer and microcontroller needed via available of serial port; (3) Data base of instructions of MCS-51 instructions; and (4) Converter, used to converting the 7 segments LED to hexadecimal form. With these kind of facilities, now in mind, the assembly and its implementation in a microcontroller especially (here) MCS-51 felt as simple and easy, even for the beginner users. From our design and implemenation efforts, there was not found any troble and fatal error. So, the system is works well. For further development, in order to take more benefit of ICT infrastructure, this kind of program via sensors needed and ASCII code converter, the system must be designed so that can be operated remotely.