Microcomputer systems: introduction to assembly programming

Giuliano Donzellini, Domenico Ponta

Analysis and tracing of a simple de-cryptographic program




The following program executes a simple de-cryptographic sequence over a given numerical table ("message" in the following). In this laboratory you will gain confidence with the instruction set of the DMC8 and you will use the debugger of the Deeds Micro Computer Emulator.

The message to be de-cryptographed is defined here:

Click on the figure to open the program in the d-McE editor. Analyse it, looking at its sequence of instructions. You should understand what the instructions do, paying a special care to the execution of the loops and to the condition of the jumps. Describe the function carried out by the program, adding a few comments to the lines of code.

You can test the program functionality in the debugger, tracing it in step by step mode. To observe the content change of the memory locations involved in the processing, you should scroll down the memory panel until the memory locations of interest will be visible (you can use also the commands available in the memory context menu).