Prototype #2 is aliiiive!

[Cyber]

I just now had another thought... Does electrical breakdown is relevant here? Technicaly it should not be, because it happens beacause of too high voltage and not because of too high PSU power. I'm still learning, so I'm not sure about these things...

[picosecond]

5 hours ago, Lorin Millsap said:

IIt’s too much power when you make a mistake and fry something catastrophically. We are looking at implementing perhaps self resetting fuses or something.

I thought we were keeping things simple.

A fuse is not going to protect any ICs from metal objects and clumsy fingers.  At best it will avoid vaporizing some main power traces that got treated to a dead short.  If someone accidentally does that, lesson learned and break out the rework wire.

[m00dawg]

6 minutes ago, picosecond said:

I thought we were keeping things simple.



A fuse is not going to protect any ICs from metal objects and clumsy fingers.  At best it will avoid vaporizing some main power traces that got treated to a dead short.  If someone accidentally does that, lesson learned and break out the rework wire.

Fuses are cheap though, even self resettable ones. I thought the main reason for fuses were fire. I agree, if you short something, there is probably damage. But also consider most of the components are through hole and socketed. So saving the traces here is probably worth the small extra expense.

[Lorin Millsap]

That is it exactly. So picture if you will soldering one of these boards yourself and you make a mistake and say for example happen to bridge a power and ground. That short may not damage any chips but it could potentially vaporize a trace.  In theory most power supplies are going to be able to detect dead shorts and shut off themselves but you can’t really rely on that because they might still allow an awful lot of current before they sense it as a short.  I for one feel that putting some kind of fuses that are some value we consider normal and safe would be better than just allowing The power supplies full output unrestricted.   Sent from my iPhone using Tapatalk

[TomXP411]

15 hours ago, BruceMcF said:

In one of the 2 "proto #2 working" videos, something is mentioned about five device spaces for four cards. I don't have time to listen to them again this afternoon, but IIRC, how that will work is not entirely settled.

I think that all of the CS lines will be present on each card slot, which makes it up to the expansion device to operate on the correct CS pin. 

This will probably mean a jumper block on the card, which connects to the correct pin on the slot. Someone could devise a PnP system that sets the correct CS line through software, but I don't see much utility in that when a 10-pin jumper block costs next to nothing.

 

 

[BruceMcF]

8 hours ago, TomXP411 said:

I think that all of the CS lines will be present on each card slot, which makes it up to the expansion device to operate on the correct CS pin. 



This will probably mean a jumper block on the card, which connects to the correct pin on the slot. Someone could devise a PnP system that sets the correct CS line through software, but I don't see much utility in that when a 10-pin jumper block costs next to nothing.



 



 

Simple cards would still be simpler if there is one device space associated per card and one handed to all of them. And that is less like to give conflicts where some card makers take shortcuts on which space their drivers address ... having the dedicated select be at card slot +3 (4-7) means they should write their driver for whichever slot it is put into.

BUT it's not a major issue, and this design makes a single slot and optional riser board straightforward for the small form factor CX16e.

 

[TomXP411]

On 1/8/2021 at 11:39 PM, BruceMcF said:

Simple cards would still be simpler if there is one device space associated per card and one handed to all of them. And that is less like to give conflicts where some card makers take shortcuts on which space their drivers address ... having the dedicated select be at card slot +3 (4-7) means they should write their driver for whichever slot it is put into.



BUT it's not a major issue, and this design makes a single slot and optional riser board straightforward for the small form factor CX16e.



 

You're not wrong, but there's always going to be That One Guy who takes the shortcut... 

anyway, I'm basing my assumption on this pinout diagram from Facebook:

 

I'm assuming that IO3-IO7 are active low when the system is addressing the expansion port I/O range. 

 

 

[BruceMcF]

Yes, I didn't have time to look the card spec up because of the exam my MBA students just took, but I read it the same way .... I'd assume from a 3 to 8 pulldown decoder with i0-i2 on a5-a7, with o0-o2 used internally. That can be pretty flat logic.

There was a time in the late 90s when I was perusing glue logic data sheets for a piece of C64 kit I never got around to building, it was well after the days of TTL, but from the TTL days pull down selects were popular because TTL pulled down harder than it pulled up. CMOS is more symmetric.

 

[Travis Bryant moore]

I like the idea of streamlining and adding new power options.