Q40 and Q60 video controller for flatscreen monitors

[Dave]

My PCB maker does castellated PCBs for no extra cost. Tech has come along way.

How would you specify that? Just let the board outline cut through pads and write "castellated PCB" in your description text file?
What surface material would they use then?

In this application, I would just put the edge cut lines across PTHs in a whole panel of these, yes. You could use the same board for two PLCC sockets and use them as a standard riser. You could go for tinned or gold plated. I personally would spring for the plating, to prevent tarnish build up. Since the Qx0 is a 21 years ago respin of a 35 years ago design, there's an actual chance it'll get handed down through the generations.

It would certainly seem that making more QX0 PCBs, but with just an extra header or two with some vital signals brought out would bring extended capabilities well into the future.

Maybe. Probably only if someone designs a new video card also. I'm uncertain about the whole 68060 or "high end" issue.

Watching my personal usage, the Q68 is so neat that I fire up my Q60 less often. The 68060 is less compatible for old software and games than the Q68. And when I need high speed as a tool, e.g. to compile large sources, the PC is faster these days.

Also what to do with the existing Q40 and Q60 boards? Just rip out the socketed chips and ditch?

It strikes me that besides a few passives and a CPLD, you're already close to replacing/updating the whole machine.

[Peter]

In this application, I would just put the edge cut lines across PTHs in a whole panel of these, yes.

For readers who are not hardware developers, PTH means "Plated Through Hole".
I still don't understand how to specify, as there is no hole, hence no PTH, just a rectangular pad.
Or would you define a pad with pro-forma drillhole and then place the edge cut so the hole is outside the PCB?

[Dave]

With modern laser cut holes, they can be any shape you want. My PCB house doesn’t even have drills any more.

[Peter]

So what would you do, just let the outline cut through the pads and specify nothing?

[Dave]

Well, I do explain my intent in the comments box, so they don’t just think I am an idiot.

[Derek_Stewart]

Well, I do explain my intent in the comments box, so they don’t just think I am an idiot.

No one thinks you are an idiot, it just sounded like cutting a big hole in the Q60 existing PCB for the new PCB section.

So do I gather that there be gaping hole in the Q60 PCB and no changes to the design.

Personally, I think the Q60 design is very elegant, even after so many years.

[Dave]

Noooooo!

Imagine a small PCB the exact size of a PLCC IC. It fits in the existing socket. It has 28 or 44 or whatever is needed pins facing up, going into a daughter card. This way you can add circuitry and the original IC to an existing socket.

The castellated PCB makes contact with the contacts in the PLCC socket.

[Derek_Stewart]

Hi,

Just what I thought,no chnages to the Q60 PCB.

So I can put my saw away...

[Szk]

Hi, I may be wrong, but I think what Dave is trying to explain is something similar (or more sophisticated) to this...
Pictures from Mr. Mark Smith in this FB thread where he describe his attempt to replace an old CPLD on a TC2068.
I hope it can help...

[Dave]

Exactly. It would fit in the socket without any SMD rework. It just provides a block of pins facing up. You put one in each of the two PLCC sockets, then the actual expansion board goes right onto it.

See how it was made as a panel - could have been 20x20 panel, and with a solder paste mask, you'd be able to lay that out ready for reflow in bulk. 400 at a time!