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May 23, 2014 AT 5:00 am

LMC – The Little Man Computer on the Raspberry Pi #piday #raspberrypi @Raspberry_Pi

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Learn about the fundamental processes underlying computing on your RasPi by using this adaptation of the classic LMC educational instruction set simulator. LMC – The Little Man Computer on the Raspberry Pi from Gordon Henderson:

This implementation is written using RTB on the Raspberry Pi and allows manual data entry via the computer control panel or you can use the built-in assembler to load files in its assembly language.

I have added some extensions to LMC to modernise it from its 1965 roots. The first is the JSR and RET instructions. JSR is Jump to Subroutine and RET is return. In keeping with the simplicity of the system, there is only one register to store the program counter for the RET address.  The other additions are for the Raspberry Pi’s GPIO. You can read a pin or set a pin to high or low. See the examples for details.

The RTB/Raspberry Pi implementation features three running modes – one is slow and runs at 10 instructions per second. This allows you to visually see the memory and accumulator changing as well as the program flow, the second is fast mode – the output register is updated, but that’s all, and finally you can single-step a program.

…The LMC is controlled by simple key-presses. On the main screen, you can move the active location (memory address highlighted in Yellow) using the arrow keys. To manually enter data or an instruction just type the numbers – the memory locations will only take the last 3 digits typed. Entering 1234 will result in 234 being placed into the memory location. Use the minus key (-) to negate the value. Pressing the Enter key moves to the next memory location….

Read More, including installation instructions and examples at Gordon’s Projects.


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