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When you start the simulation you will see the CPU with the program counter, instruction register, memory address register and the Accumulator on the left of the screen, ROM on the right and the address bus (blue), data bus (green) and the control bus (red) in between. Refreshing the page, which simulates power-down followed by power-up, does not change the contents of ROM because ROM is nonvolatile. However, the data on the busses at this point is random. This simulation is for a fictitious microcontroller with a very limited instruction set which is given in the table below.
The following short program is assembled into machine code and placed in ROM. LD A, 05H As can be seen in the simulation, ROM contains:
Step through the simulation by clicking on Next -> and watch as each instruction is decoded and executed. |
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Copyright (c) 2005-2013 James Rogers
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