Parts, parts, parts...

A project log for Discrete YASEP

a 16-bits YASEP computer (mostly) made of DIP/SOIC chips like in the 70s and 80s... with 2010's twists!

yann-guidon-ygdesYann Guidon / YGDES 10/26/2015 at 23:270 Comments

Circuit design is like speaking a language. You have vocabulary (parts) made of letters (transistors and gates), grammar (how a few parts interact to provide a macrofunction), sentences, paragraphs... The semantic is what the whole is meant to do. In the end, there is the effect on its environment, what it takes from and brings to the universe...

Going further, building a computer is like poetry. There are different sizes and scales (haikus or epic medieval ballads) but there must be style, elegance, purpose, function, structure. This discipline uses all the known skills of the maker and it's also a self imposed exercise with constraints, hopefully aimed at creativity (and hopefully fun).

For computer design, the constraints are the basic building blocks that you can access (like "back in the days, this little part used to cost $20") or that you choose. For this "discrete YASEP" the choices depend on:

Speed is not a consideration as long as it is not ridiculously slow.

Naturally the parts are mostly in the 74 logic family.

The use of 74HCT shows that the technologies are mixed (CMOS/TTL). Supply voltages too may be mixed, a 3.3V device can send data to a HCT@5V. It will depend on availability...

So basicly we have a set of voltages, currents, speeds, to talk with. What is done to these signals is the other dimension of the design: now we'll talk about the logic functions. Let's review the "building blocks" that will be used all over the system :

The Multiply operation will be implemented with a (E)(EP)ROM array or a RAM chip (it will be fun to program the code that fills it ;-) )

The Shift operations are a different beast. I suppose I'll use an Omega Network topology (See Michael Riepe's research for the F-CPU 15 years ago). This unit will use a BUNCH of 2to1 multiplexers... I'm not sure the '157 will do but who knows.

Memory : for the DIP prototype, I have many 32K×8 static "cache" SRAM in narrow DIP24/28. It's fast memory (about 15-25ns) for the Pentium motherboards, using 5V and they get warm easily. I used to pull them from discarded motherboards around Y2K... They are way too fast for this computer but they are just the right size and capacity, and I got a bag of them. The SMD versions will use lower power devices.

I'll update this log when more "significant" circuits will appear on the radar.