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RaSCSI Development Thread


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10 hours ago, NF_ said:

I see the appeal to have it powered by the SCSI bus, but I don't see how it can be done practically.

 

The Mac II, SE and Plus use an NCR 5380 SCSI controller. The controller outputs have a max voltage of 2.4v, and 48mA. In addition to the low numbers, the SE, Plus and II don't provide termination power.  Even if there was a way to scavenge power from some of the other lines, The Pi Zero W needs at a minimum 80mA, and to get the power draw that low, you sacrifice a bunch of functionality.

 

I think powering stuff via the SCSI ports would hinges on termination power being available. But since the computers this is initially targeted at target machines don't provide TERMPWR, building any circuitry to leverage it, and building a environment to boot up quickly would yield very little gain.

  

What could be useful is a separate unit, something akin to a parallel port pass through dongle type thing.  It could scavenge the TERMPWR and feed it into the RPi via an external cable, or whatever. With a separate unit, it's modular, and could be used for this or any number of other projects.

I'm still reading about this, and wondering if I'm mis-reading or misunderstanding something.  I'll check the TERMPWR on my SE this weekend. If it's there, I should see 5v on pin 25. 

 

I've attached the NCR 5380 SCSI Interface Chip Design Manual for those interested, or you can find it online here.

NCR_5380_SCSI_Interface_Chip_Design_Manual_May85.pdf

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@NF_ My understanding is that the SE and II both provide SCSI term power, and the Plus is the only Mac that doesn't (fun fact:  the circuits for providing it, to my knowledge, were partially implemented, but it was disabled from the factory.  It can be enabled by adding a couple missing components I think, but the Plus' SCSI implementation isn't entirely standards compliant, so it may or may not work as expected.)

 

c

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Yes that’s correct, it’s trivial to add termpwrto a Plus.  Plus SCSI can be flakey in various minor ways (and the earlier Plus ROM revs have an issue that can lead to getting stuck at a black screen on soft reset if trying to boot from a SCSI device) but none of them are too major and basic config tweaks can be used to get a SCSI2SD working with a Plus after a bit of hassle.

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13 hours ago, CC_333 said:

@NF_ My understanding is that the SE and II both provide SCSI term power, and the Plus is the only Mac that doesn't (fun fact:  the circuits for providing it, to my knowledge, were partially implemented, but it was disabled from the factory.  It can be enabled by adding a couple missing components I think, but the Plus' SCSI implementation isn't entirely standards compliant, so it may or may not work as expected.)

That's interesting.  Thank you for clarifying.

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Its ALIVE!!!! RaSCSI 2.2 is up on Tindie!!!

https://www.tindie.com/products/21131/

 

For all of those who are still interested in getting started with RaSCSI, feel free to grab one. 

 

For 68kmla friends, there is a promo code: "LABORDAY2020" that is good through Tuesday, Sept 8 for $10 off. 

 

I've never done this Tindie thing, so let me know if there are issues with the listing.

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8 hours ago, landoGriffin said:

For all of those who are still interested in getting started with RaSCSI, feel free to grab one. 

Ordered!! Thanks for putting it all together! :ii: The parts I ordered arrived weeks ago but the PCB manufacturer delayed the boards over and over (grumble grumble) so I don't have them yet. >:(

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8 hours ago, sonique6784 said:

Thank you so much for putting that together!

Is there any chance to get it ship to Australia? (Currently not supported)

Australia is added! Please let me know if other folks need different countries. I was just too lazy to try to predict what countries to calculate shipping for!

 

If you want to know what the shipping rate is, I'm using USPS Priority Mail Small Flat Rate Boxes. Its shipping from Iowa in the US.

 

Also, if you want to order multiple, message me, and I'll figure out how to combine shipping.

Edited by landoGriffin
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On 8/2/2020 at 11:09 PM, Torbar said:

The SCSI2SD V4 uses a 7406 which are <$1 each, maybe that's a possible alternative?  Looking at the datasheet it appears to be able to sink 48ma

 

https://www.digikey.com/product-detail/en/texas-instruments/SN7406DRG4/296-48954-1-ND/8635017

Hey @Torbar, I was thinking about your suggestion and didn't want it to go unnoticed.  Looks like the SN7406D can sink 40mA, which is closer than the 245 only sinking 20mA, but still not within spec (48mA).  Another issue is it provides six buffers/drivers versus the eight on the 74xx245 and 74LS641-1. So the pcb would require some rework, but still not meet the SCSI spec.

 

But it is a good suggestion, and I have added it to the transceiver comparison page in the wiki.

 

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8 hours ago, Byte Knight said:

Any idea if the RaSCSI would work with an Apple II w/SCSI card?  I could see it as another HD option and the GS supports CDROM.

The hardware should be compatible. But, there might be some software tweaks to get it working. The Mac is picky about what firmware types are reported by the SCSI device, but I'm not sure about the Apple II.

 

I have also tested the hardware/software with a Ubuntu 20 system, and it works fine.

 

I'm going out on a limb that if you tried it, there is a forum full of people who would be willing to help troubleshoot if it didn't work :-) 

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Nice to see that it can come as a kit... solder paste is use it or loose it and this would probably make a good project to use up some of my spare bismuth-tin-silver solder paste.  Especially, the "through hole reflow" technique uses quite a bit of paste.

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Now, a big curve-ball question... is it possible for a single board to combine both the functions of RaSCSI and pi-parport?  And, additionally, provide both host and device modes for parallel port communications?

 

https://github.com/worlickwerx/pi-parport

 

Yes, the DB25 connectors on both interfaces are that tempting, not to mention that some historic SCSI devices were implemented to also be able to communicate via a parallel port.

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