Real-Time Clock Display in x86 Assembly (TASM)

Overview

This program continuously fetches and displays the current system time in the format HH:MM:SS on the screen using 16-bit x86 assembly. It updates every second, clears the screen before each update, centers the time display, and exits cleanly when any key is pressed.

Features

• Uses DOS and BIOS interrupts to get the system time and handle keyboard input.
• Converts binary time values to ASCII for display.
• Clears and refreshes the screen on each update.
• Centers the time display on an 80x25 text screen.
• Exits gracefully on any key press.

Requirements

• TASM (Turbo Assembler) to assemble the .asm file.
• DOSBox or a compatible DOS environment to run the executable (since it uses DOS interrupts).

How to Assemble and Run

1. Assemble the code:

   tasm clock.asm

2. Link the object file

   tlink clock.obj
   

3. Run the executable in a DOS environment like DOSBox

   clock.exe
   

Code Highlights

• System time retrieval: Using int 21h with ah=2Ch.
• Keyboard check: Using int 16h to detect key press without waiting.
• Screen clearing: Intended to use BIOS scroll window function (may require fix).
• ASCII conversion: Custom subroutine to convert binary values to two ASCII digits.
• Cursor positioning: BIOS interrupt to center output.

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Output

This is the screenshot of the program output.

For detailed explanation of the code, see the Documentation.