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I looked on Mouser for an ISA slot connector. I found a whole backplane ?? for $28+. I looked other places. Briefly. I found nothing.

Looking on Mouser for a PCIexpress connector, however immediately gave me this:

PCI Express / PCI Connectors 98P CARD EDGE ASSM VERTICAL

A 98 place socket for $0.78 quantity 1, $53.40 for 100. A common, inexpensive part. Nice.

I suggest that the PCIexpress (x8) connector would be more appropriate for Commander X16, just based on availability.  98 pins may seem like a lot for an 8/16 data bus, but:

  • The 65C816 has a 24 bit address space.
  • For EMC and signal integrity reasons, every signal should have a return path (ground). Adding a dedicated return for every signal will make the bus much quieter.

If we were to expose all 38 signal pins from the 65C816, plus the extra de-multiplexed 8 address bits, and then give every signal a ground, that leaves just four pins for Vcc. That doesn't seem all that extravagant to me. I'm not saying we should directly expose the full CPU bus, but having room to choose what we want to share is A Good Thing(tm).

Any (weak) argument that this would tempt people to insert PCI express cards would also apply to ISA connectors. You can just reverse the socket or change the distance from the edge of the motherboard so a normal PCIe card would not even fit.

I'm not suggesting that we support PCIexpress, just that we use the same mechanical connector because it is cheap and readily available.

 

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I looked on Mouser for an ISA slot connector.



I'm not suggesting that we support PCIexpress, just that we use the same mechanical connector because it is cheap and readily available.


Please correct me if I am misunderstanding anything, but when you say “we“ do you mean the developers?

If you are referring to the first model we will be releasing, it is far too late to be discussing changes to the expansion slot form factor. We are trying to lock down a third and final prototype before production. Sorry.

Lots more info in the FAQ in case you missed it.


Perifractic, X16 Visual Designer
http://youtube.com/perifractic
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10 hours ago, Terrel Shumway said:

I looked on Mouser for an ISA slot connector. I found a whole backplane ?? for $28+. I looked other places. Briefly. I found nothing.

What does that have to do with anything? The slot isn't an ISA slot connector.

And the owner of the CX16 doesn't really need to source the slot connector ... if they are doing a hobbyist DIY card, they will need the circuit board with the traces defined correctly and they'll be good to go.

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On 3/2/2021 at 11:05 PM, Perifractic said:

Please correct me if I am misunderstanding anything, but when you say “we“ do you mean the developers?

If you are referring to the first model we will be releasing, it is far too late to be discussing changes to the expansion slot form factor. We are trying to lock down a third and final prototype before production. Sorry.

ooops!   =:-0

I guess I was subconsciously talking to the mouse in my pocket...watching too many of Rick Hartley's videos on designing high-speed PCB Assemblies.

If I ever build my 8-bit dream computer, it will have an expansion connector with a 24-bit physical address space and every signal surrounded by ground returns. (And it will probably boot to FORTH instead of BASIC.)

Yes, it would have been nice to have been where I am now three years ago and been able to work on the first prototypes, but wishing won't make it so. 😞

And yes, once you publish a spec, it becomes really hard to change it. The S-100 bus was horrible*, but it mostly worked and it created an amazing ecosystem that spawned an industry and survived almost a decade. I hope that CX16 does the same and becomes a dominant platform in the retro space. That requires that you eventually say "it's done" and keep your promise to never break compatibility. Part of the joy of retro is working around limitations of these set-in-stone design decisions that you curse your younger self for making.

Since you are only targeting 8MHz and don't need to pass FCC, it won't matter anyway.

Thank you for what you have done. Even playing with the emulator is fun.

-- Terrel

* so was the ISA bus that followed it. And that survived even longer.

 

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On 3/3/2021 at 5:07 AM, BruceMcF said:

What does that have to do with anything? The slot isn't an ISA slot connector.

And the owner of the CX16 doesn't really need to source the slot connector ... if they are doing a hobbyist DIY card, they will need the circuit board with the traces defined correctly and they'll be good to go.

I was just looking around for a cheap connector for my own hobbyist DIY card idea. If you want to share your hobbyist DIY card, you need to match the hardware that others have.

What I should have done was spent more time reading the forums and discover that the current hardware has a 50 place connector like the Apple ][ used, as Kevin Williams pointed out.

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Posted (edited)
18 hours ago, Terrel Shumway said:

I was just looking around for a cheap connector for my own hobbyist DIY card idea. If you want to share your hobbyist DIY card, you need to match the hardware that others have.

What I should have done was spent more time reading the forums and discover that the current hardware has a 50 place connector like the Apple ][ used, as Kevin Williams pointed out.

Yes, that's likely part of how they settled on the 50 place connector, that it's actually still in production. IIRC, the fact that it was easily available was mentioned when the slot was first introduced.

It's not like it is still in production for Apple II's, but I know that in some industrial control applications, you are operating in a dirty environment with a lot of vibration, and I would not be surprised if those wider traces can be really handy for keeping the machine controller up and running in that kind of environment.

A spin-off benefit is that it is also compatible with some retro 70s and 80s board creation techniques that wouldn't work with something like a PCI slot.

Edited by BruceMcF

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