Random number generator in assembly code

Question

Does anyone know how to code a 8 bit numbers to be randomly generated in assembly code?

I'm using ATmega8535 with Atmel AVR Assembler with the Debug of AVR Simulator. (AVR Studio 4)

Sorry i am new to this and any help would be appreciate Thanks

Answer 1

It really depends on what you mean by random. If you just want a sequence of numbers that are predictable but have statistical randomness then the simplest to implement on a microcontroller is the linear feedback shift register. An example of an implementation in assembly on a PIC device can be seen here.

Variations with better cross-correlation properties are Gold-Codes which are a bit more complex but rely on the same principle. There are also a lot of other algorithms, but it really depends on what sort of statistical properties you require.

If you need something with a high level of entropy (i.e. can't be predicted) then a novel way is to use the device's ADC to sample the voltage on a reversed biased diode junction. The noise generated by this is a robust source of entropy. However, you need to be careful that you don't introduce any order into the system by accident so some care in the design is needed.