(Not sure if this belongs here or education, as it's not actually raspi related, I think it belongs here)
Inspired by Rurwin's comment about the 74181 Arithmetic Logic Unit in another thread and an urge to prevaricate over coffee while having a break I've decided to have a go at building a 4 bit computer.
Sadly the 74181 is no longer in production so I've bought myself one of these SN74LS181NICs instead....(edit -dinnngg ... I've just noticed the similarity in serial number, coincidence?)
So in essence it allows arithmetic and logic inputs on two 4 bit words (inputs A0, A1, A2, A3 and B0, B1,B2, B3) by setting 4 control / function select bits (S0, S1, S2, S3) and a 4 bit output (F0, F1,F2,F3) and two carries (Cn and Cn +4 (not sure how these work yet))
I've also bought a load of flip flops to make some static RAM with and some assorted ANDs, NORs, XORs and so on which I am sure will come in handy.
So, step one will be to to just manually try different operations like addition, subtraction etc. with LEDs on all the F and C output pins. Just to prove and facilitate understanding.
Step two I think will be to try to make some RAM with the flip flops and then begin to use this to create part of a read, write and execute cycle.
Step three will be to use the knowledge gained from one and two to try to understand how to go about building a controller and after that some sort of data storage / input / output system.
It would be nice if I can have a plan in place for September when the new school year starts as I would like to offer a kit and information for extracurricular clubs so I can hit the year running.
Duty calls, more soon...