Update: 10/06/2021
Docu Download CPU's Theory

8 bit CPU simulation

How does a processor work?
What about binary code and assembler?

Even when looking at simple historical processors in extracts, the beginner is left with gaps in understanding due to the initially unclear links of the complex system.

The frequently used "MOTOROLA M68000 FAMILY Programmer's Reference Manual" contains 646 pages! The comparable manual of the HC680 only needs 5 pages, but not all details are documented. This is also not useful, because the simulation with its help allows to fathom details if necessary.

The entire HC680 system is manageable in a reasonable amount of time.

The basic construction and instruction groups allow an easy start. Multiplication by Booth (assembler MUL) and division with remainder (assembler DIV) are already somewhat more complex. There are additional tooltip helps during their execution.

Is a relevant problem solvable with such a minimal system?
Sorting a small file with recursive quicksort is one answer!

Data of the system

  HC 680 fictive
Processing width:
  8 bit data and addresses
Command length:
  1 byte
Address space:
  256 byte
Clock pulse:
  single step, 0.1Hz to 255Hz, unbraked
  4 general registers with shadow register, start address (ST), instruction register (IR),
  instruction counter (IC), status register (SR), stack pointer (SP)

  Negative (N), Zero (Z), Overflow (V), Carry (C)
Arithmetic Unit:
  Arithmetic Logic Unit (ALU), 8+1 bit sign extension for addition, multiplication
  according to Booth, division with remainder, ALU can be represented bitwise

  decimal from -128 to 127
  8x8 maxipixel display, 8 byte shared memory
Input - Output:
  keyboard character, decimal, hexadecimal, - output also binary
  keyboard characters, decimal, hexadecimal, binary
  3 - changeable during program run
  any section in selectable file
  40 mnemonics, 57 commands by addressing modes

example representation quicksort (recursive) of the file input.hcx

background RGB default values 238, 238, 211 (Note: German Windows Editor displayed)


04/16/2014 - simulation minimal 8 bit processor system - 256 byte RAM

Imprint (DE)