Transfer Register PCB (Hand routing) - Making an 8 Bit pipelined CPU - Part 52

I start this video discussing the next steps on the project, there isn't that much further to go before the core processor is fully functional. I'm excited!

The bulk of this video is hand routing the Transfer Register PCB. It wasn't going to work with the auto router techniques I had been using on the other boards. That was originally over 9 hours of footage, so with a lot of editing you mostly just get the commentary.

This is the video plan at present, there will be at least one mailbag video and I'm also overdue an update to the project introduction video (it only covers half the project now). I’ll try not to get distracted.

Memory Bridge
Connect Flags to Pipeline
Flow control (May be merged with above)
Solder Transfer Register PCB (+test)
Main memory (Ram!)
Temporary Output Peripheral
Stack + Call and Return
Programming Example
Flashy Demo

[martink.]

No auto-routing at sight, hell yeah beautiful! Was waiting for it so long :) Not the easiest board for first manual routing, but definitely worth it.

[mgeo]

It's usually frowned on to put vias on pads if you are having PCBs manufactured (or using stencils and solder paste), as the solder runs through the via and there isn't enough left to make a good joint. If you're hand assembling, it doesn't matter.

[JohnDlugosz]

Designing a 1960's minicomputer using 1970/1980's components and 21st century CAD/CAM is a whole lot easier than it was originally!
I remember in the early 80's making a PCB meant doing your own acid baths and drilling holes, and layout was using black tape and stickers on clear plastic. The idea of doing that on a PC and printing out the mask, even if it has to be 2x or larger scale, was tantalizingly close, thinking that such a program ought to be doable.

[DustinWatts]

There is something strangely relaxing about watching a board being routed nice and symmetric. It must be my OCD 😁

[BillySugger]

For your first major hand routed board you did a very good job there. _Much_ better than an autorouter could have. My biggest suggested improvement is ground continuity, avoiding vias to ensure ground connections. It’s better to via many, many signals than to via ground between devices. Your flood full will mitigate that to some extent, but around the multiplexers it’s a bit of a mess. I hope that doesn’t end up being a bandwidth limitation for your CPU as it has the potential to run at a respectable speed when fully on PCB.

[jerril]

Great work, it must of taken hours. Congratulations on no training wheels :) It is getting very exciting. It will be interesting to see the bits shuffle around once there is RAM. Thanks James

[jessefinnegan]

Now I see why circuit board routing can seem chaotic at times. You really have to work with the pass thru radius in interesting ways.

[IslandHermit]

You don't need the RAM module to be Turing complete. Your existing GPRs are sufficient.

[twobob]

Totally worth it. Can tell you are getting excited. Worth it.

[petesapwell]

Incredible work…Really impressed with the hand routing, well blummin done!

[tinygriffy]

wow, i tip my hat... i wouldn't even have attempted that with a browser based EDA software ^^
have you ever considered taking a look at KiCAD ? I think it has some features that could come in handy doing this kind of routing.
(edit: for example creating track arrays ;))
anyhow... very nice work, thanks for sharing !
btw.. i'm new here, came over from unexpected maker ... good thing you joined the live stream ! ;)

[sillymel]

(0:45) I love that little effect you did there!

Is the transfer register schematic not on your EasyEDA page? I don't see it there.

EDIT: What would the "REG_TX_AMODE" line have been used for if it actually ended up getting used?

[DavidWatts]

I wasn't sure if I would enjoy watching 30 minutes of routing but I really really did. I wish you had clicked on those bell notifications sooner though 😂 Looks ace mate.

[mgeo]

James, am I right in thinking that the 'Assert A Mode' does nothing on this board? I can't see it doing anything on the schematic?

[edgeeffect]

That's a funny idea... When people put DIY or retro hardware stuff on YouTube. The typical lesser-troll comment is to say "yes... but will it play (insert name of currently most popular game here)?". So it's good that you'll be able to reply "not quite... but it will play (insert game you've written here)".

[edgeeffect]

How long did that take in real time? I've had a few goes at making MUCH SIMPLER PCBs than this and haven't been able to handle the frustration of having to hold a mouse for so long. After watching this my only thoughts were "You da man!!!"

[PeetHobby]

Why did you build everything so big? 75% of the PCB's are just wasted empty space. Why not use pcb mask to draw how the computer works, like where the busses are, and how they are connected, with arrows and bit sizes and so, and what the components do inside, etc?
Edit: You don't have to connect all the GND traces first if you use ground plain. ;)