8 Bit Breadboard CPU

Finished the 8 bit ALU design schematic based on @roelh 's square inch ALU design.  Includes design for the input register which has a control signal to load.  It's output is tied to the B input of the ALU.  The data bus will be the A input for the ALU.  The output register design is included, whose input is tied to the output of the ALU. It has a control signal to output to the data bus.  There is also the logic to set the flag lines (CArry, ZERo, and NEGative).  The Status register (not in this schematic) will have a control input that set's weather they flags are stored or not.

https://upverter.com/2-Zons/2f903c2bed9cef6d/8-bit-ALU-w-input-and-output-registers/

Reworking things a bit based on some excellent feedback.  I will be using an 8 bit ALU based on @roelh 's 4 bit ALU.  Instead of having hardwired to the AB, XY registers, it will have an input and output register.  It will then use the data-bus and it's input register for inputs and it's output can go anywhere one cycle later.

I have been thinking about addressing modes for instructions.  I think I will keep it to direct, register, and immediate.  I have been thinking about offset addressing, but with only an 8 bit ALU I will run into page overrun problems.  Better to do this in software I think.  I don't think it's worth building a 16 ALU, as this would introduce a whole new set of problems in this new design, and I have to remember to try and keep it simple. 

I've updated my block diagram, working on the new instruction set.  These are both a work in progress and very flexible.

https://docs.google.com/drawings/d/1BW84zwO5effvYcdKjxzyki9cuvuHsM98z6nAamw4iTM/edit?usp=sharing

https://docs.google.com/spreadsheets/d/1kbxYGDeIOszgvjPYRdes-bELOBlojT_tjxe_RD9MVUQ/edit?usp=sharing

Completed V1.0 schematic of one of the 16 bit registers.  There will be two of these (AB and XY)  Created an Upverter project and added to the links.

https://upverter.com/2-Zons/1a1b5dbb645ac3ba/8-Bit-Breadboard-CPU---AB-Register/

Received first shipment of logic chips (see photo) as well as an assortment of switches, and adruino which I will be using to program the EEPROM'S.  Still waiting on a few more items before I can start tinkering.