Functional Operation

Day 20

     Today I finally got some work going on Fritzing and hope to have those files to share later this week and between that and the anticipated arrival of the first shipments of relays should be able to get back to work on the details of the clock circuit. For today, though, I will be focusing not on any specific circuit but on the operation of the overall system as I understand it to this point.

     The overall function of this computer starts with a program being inputted  by hand byte by byte via the 8 bit data bus. At the same time an address is assigned to the instruction being entered on the 16 bit address bus. once the program is entered into memory the initial value can be loaded onto registers as needed and then the clock circuit is unfrozen and the program is allowed to run in sequence until either a halt function is called or the clock circuit is refrozen. Arithmetic functions are loaded onto the B and C registers the result of this function is loaded back onto the data bus and inputted to whichever register needs it next then the increment register will signal to load the next instruction which will repeat the process. There are several registers on besides the B and C registers each has a specific function which almost all involve storage for a time for 1 reason or another. Registers such as the M1 and M2 or J1 and J2 or X and Y registers can also access the 16 bit address bus and in the case of M and XY they can load data onto the data bus as well J can only read from the data bus there is an incrementing circuit feeding into the Program counter solely for the purpose of advancing the program instruction set. While there are several other details such as control lines they add little to the discussion of the overall function of the computer. 

     Wednesday we will be going into more depth with the function of the ALU even more so than before and with any luck schematics will be forthcoming as well.

      As a note on the Fritzing work I am still looking into building a set of custom parts but for the moment I have decided to go with individual discreet components. This will work in the short term for getting schematics drawn up and shared and will be refined as time goes on. So for the now my relays are made up of a coil and 4 SPDT switches simply laid out to resemble a relay of the type I desire which will work quite well for schematic visualization but will not allow us to leverage the full power of the Fritzing platform though for a project of this scale I suppose AutoCAD would be better suited for the rest of the layout types. If you haven't used Fritzing for a smaller project I highly recommend it as it will allow you to take a breadboard project and pull a schematic and PCB layout out of it with minimal work or take a schematic and prototype it well. It is a powerful tool that is free and rather well built.