Kerm, please excuse my mild exaggeration, and I MEANT to say that for every output you need ONE gate with several inputs. The gist of what I was saying is that even basic signal decoding takes MANY transistors. Thanks for correcting me before I corrupted his (or her... sorry Ashbad if I got that whole thing wrong.) mind or anything.
@Ashbad
In the long run, an FPGA would be the cheapest for building you own CPU. However, instead of learning soldering, PCB layout, and other useful skills, you would need to learn Verilog, software design, and stuff. Either way, you need to write some things out that you want to do that are feasible.
If you are at all serious about this project, read this book: http://www.scribd.com/doc/13388965/Build-Your-Own-Z80-Computer
It takes you through the ENTIRE process of building your own computer, from the power supply to a CRT monitor. Most of the parts are common and still available. The ones that aren't, I could help you find an alternative. You don't really BUILD your own CPU, but I'll be darned if you don't learn a lot by trying! Think about it...
Some basic criteria I recommend you try to attain are:
1) Build a 8 or 16-bit CPU
a) 4 registers the same size as the CPUs word-size
b) Register processing commands that can put data in and out of the registers.
c) At least 3 ports on the CPU that you can take data from the register and send out so you can have keyboard and video.
d) You need the basic 4 operators add subtract divide and multiply. Tips for multiply and divide are to use shift algorithms so you can multiply and divide by 2.
e) You need a clock that can keep the CPU running at a set speed. Paper is only cool for prototypes.
2) Build a motherboard so you can USE said CPU.
3) Debug and reprogram, or if you decide on logic chips, do what I did and buy a desoldering iron and desolder 200 hours worth or work to start fresh... (Wire wrap is easier to tear apart and stuff, and is a lot like a solderless breadboard in construction...)
And please excuse my excitement over meeting someone with the same daft idea I had! I really do feel like I'm coming on strong with advice! Overall, have fun building it if you continue.
@Ashbad
In the long run, an FPGA would be the cheapest for building you own CPU. However, instead of learning soldering, PCB layout, and other useful skills, you would need to learn Verilog, software design, and stuff. Either way, you need to write some things out that you want to do that are feasible.
If you are at all serious about this project, read this book: http://www.scribd.com/doc/13388965/Build-Your-Own-Z80-Computer
It takes you through the ENTIRE process of building your own computer, from the power supply to a CRT monitor. Most of the parts are common and still available. The ones that aren't, I could help you find an alternative. You don't really BUILD your own CPU, but I'll be darned if you don't learn a lot by trying! Think about it...
Some basic criteria I recommend you try to attain are:
1) Build a 8 or 16-bit CPU
a) 4 registers the same size as the CPUs word-size
b) Register processing commands that can put data in and out of the registers.
c) At least 3 ports on the CPU that you can take data from the register and send out so you can have keyboard and video.
d) You need the basic 4 operators add subtract divide and multiply. Tips for multiply and divide are to use shift algorithms so you can multiply and divide by 2.
e) You need a clock that can keep the CPU running at a set speed. Paper is only cool for prototypes.
2) Build a motherboard so you can USE said CPU.
3) Debug and reprogram, or if you decide on logic chips, do what I did and buy a desoldering iron and desolder 200 hours worth or work to start fresh... (Wire wrap is easier to tear apart and stuff, and is a lot like a solderless breadboard in construction...)
And please excuse my excitement over meeting someone with the same daft idea I had! I really do feel like I'm coming on strong with advice! Overall, have fun building it if you continue.