[GreenKeys] 8-Level TD?

[Javier Albinarrate]

Hi Cory!

Well I already spammed your mailbox with all the pesky details of my 
project :)
In any case, for the records I suggest the following approach instead.

Have lemons? make lemonade
Forget 8 bits, who needs them? Use 6 bits with 5 bits I/O.

1- 6 bits architecture: 6 bits data 12 bits address
2- 6 bits instruction set with the following characteristics:
     - You need an extremely well thought instruction set, as baudot is 
not very binary friendly
     - Avoid special characters, like LTRS & FIGS
     - Most common actions in the LTRs range (single word because you 
use no shift)
     - Jumps and not so often instructions in the FIGs range (2 words)
     - Optional extended set (using just 1 instruction in the FIGS 
range, extends another 8 instructions with an extra decoder)
     - You need to think in detail each instruction to make it fit in 
the available ranges, and you need to remember that you can use any bit 
order for decoding, it is arbitrary (you need to tame baudot)
3- The brain
     - A resettable sequencer of 10 steps
     - A couple of muxes and demuxes, for instructions and addresses
     - A matrix of sockets, where you plug diodes 1N4007. Voilá... you 
have microcoding. That is the core of the design, because it makes 
everything EASY and FLEXIBLE.
4- IO:
     - Dulpex current loop for IO to the TTY in 5 bits. (otherwise with 
everything in a single loop it is a mess to control)
     - 6 bits buffer out and another 6 bits buffer in using relays.
     - You need to keep the SHIFT status and eventually insert / remove 
the LTRS and FIGS. This is just a little logic block.
     - Option A for sequencing: fast reed relays. Option B: Dekatron 
with vacuum tubes (lots of triodes there, probably cheap russian submini 
triodes would do it).
5- RAM:
     - Cheap option? Solid state
     - Bulky option?  Latched relays (I am lucky, I have 1k of them)
     - Weird option? Neons (many cheap russian IN2 and quite a few tiny 
russian thyratrons)
     - Magnetic option? Core. You can get loads of ferrite cores for no 
money, but it will require a lot of solid state to drive and address.

Regards!

Javier
LU8AJA




On 22/11/2013 15:15, Cory Heisterkamp wrote:
>
> Hey Guys,
>
> Looking for some brainstorming here. For the last couple years I've 
> been planning on building a computer entirely out of relays, with 
> minimal support from vacuum tubes, Dekatrons, etc. But no transistors 
> or IC's allowed! I have most of the design worked out and plan on 
> using my ASR33 for the terminal. Life would be so much simpler if the 
> communication were parallel, but that feels like a bit of a cheat (I 
> see why Flexowriters were so popular back in the day for computer 
> work). I have a Model 28 Receiving-Selector which was Teletype's 
> version of a serial-to-parallel converter. Did they ever make an 
> 8-level version?
>
> My idea is this... Basically, my output buffer holds a byte at a time 
> in 8 relay latches. When ready to send my data out to the world, the 
> holding magnet of the distributor could release, the distributor would 
> effectively "sample" the state of each of the 8 latches, and as it 
> returned to the home position, trips the reset line on the buffer to 
> clear it and it's ready for the next byte to be loaded.
>
> The trick is finding an 8-level piece of equipment to start from. Any 
> thoughts?-Cory
>
>
>
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