B. Demonstration Screen
Chapters 4, 5, and 6 of the multimedia system employ the Demonstration screens to display the micro-operations involved in:
the fetch/decode/execute cycles of a set of predefined machine instructions;
a memory access;
the CPU simulation.
The animation displayed on the demonstration screens is intended to make teaching machine level computer concepts easier. The operations are demonstrated through the graphical movement of information from one component of the computer to another. This enables the learners to observe and understand the micro-operations corresponding to the selected set of machine instructions.
For example, when the learner activates the “Chapter 5 Demonstration of the Instruction Cycle of a Computer” button from the Main Menu screen given in Fig. 1, the system first requests the user to choose one of the three cycles, namely, the fetch, decode, or the execute cycle. The system, then, demonstrates the micro-operations involved in the cycle that the user has chosen using the graphical movement of information (instructions or data) from one component of the computer to another. For example, if the learner requests the fetch cycle demo, the system first shows the graphical movement of information corresponding to the following sequence of micro-operations of the fetch/decode cycle:
MAR Formula PC
Load the address of the instruction from the program counter (PC) to the memory address register (MAR).
MDR Formula M[MAR]
Read the memory location pointed to by the MAR and store the instruction in the memory data register (MDR).
PC Formula PC + 1
Increment PC to point to the next instruction.
IR Formula MDR
Transfer the instruction from MDR to the instruction register (IR).
EAR Formula IR (Operand)
Transfer the effective address of the operand from IR to the effective address register (EAR).
The system then displays a summary of the sequence of micro-operations the computer has executed in order to complete the fetch cycle and the final contents of the registers that have been affected by the execution of the fetch cycle as shown in Fig. 3. The learner can then request the system to repeat the demonstration of the fetch cycle, or go on to the demonstration of the execute cycle of one of the predefined instructions. The learner can also choose to return to the Main Menu, the Welcome Page, or exit the system.Fig. 4 shows the screen that is displayed at the end of the execute cycle of the LDA (load accumulator) instruction.