Internal BlueSCSI, external RaSCSI, and termination question

[karl]

I'm using both a BlueSCSI and a RaSCSI with my SE/30 and I'm not sure if there's something wrong with my setup or if I'm just not understanding SCSI termination properly.

My BlueSCSI is connected with the internal hard drive cable to the 50 pin connector. My RaSCSI is connected to the Mac's external DB-25 port. If I have both connected and have termination enabled on both the BlueSCSI and RaSCSI, the Mac doesn't boot. If I turn off termination on the BlueSCSI but leave the RaSCSI's termination switches on, I can boot and mount volumes on both just fine. Disconnecting the RaSCSI cable and leaving the BlueSCSI connected internally with no termination makes the BlueSCSI not able to boot the Mac, as I would expect.

Is it not possible to have the BlueSCSI installed internally, and also have external SCSI devices like the RaSCSI connected only some of the time, without needing to open up the SE/30 and remove the BlueSCSI's termination jumpers each time I want to connect the RaSCSI? I assumed there was a separate SCSI chain internally, since the old spinning hard drives didn't require you to open up the Mac in order to connect an external SCSI device. Did the old hard drives autodetect whether to enable termination or not, or am I missing something here?

 

[Byte Knight]

I had the same problem with running an internal BlueSCSI and external RaSCSI, and I wasn't able to figure it out either. As I recall, if the RaSCSI was off it wouldn't boot either...

 

[luminescentsimian]

hmm, sounds like over-termination. Both ends being terminated is proper, but I suspect one or both of the emulators aren't capable of sinking enough current to drive a bus terminated on both ends. The new chips are too power efficient, they aren't made to slosh around as much power as those of yester-year. The short to non-existent cables usually used with them exacerbate the problem.
My 2am back of the envelope calculations say that a single 220ohm termination resistor can supply up to almost 23mA of current to the SCSI pins, which is less than the 25mA that the BluePill is rated for. But having 220ohm resistors on both ends drops the ideal resistance to 110ohms, which with 5V termination power could supply 45mA to the pins and swamp out the signals the BlueSCSI is trying to make.

huh, it looks like two RaSCSIs might work. Because the Pi can only sink 16mA itself, and even then probably not on enough pins at a time to be usable, the RaSCSI uses 4 Ti SN74LS641-1 bus transceivers that are rated up to 48mA to actually drive the SCSI bus.

 

[Hurry]

Hi, did anyone get anywhere with this? I am attempting something similar - I have a Classic II with a working internal HDD. I'd am attempting to mount images from the RaSCSI as additional drives (mounted to ID 4 and 5) in hopes of transferring some files but no dice.

 

[yock1960]

This may not help, but @luminescentsimian response above has appeared to help me. I have a SCSI2SD mounted internally on my LC475 and have been trying to use a BlueSCSI externally, to use to transfer large files to the LC475, since it's much simpler to modify a drive image in an emulator, then copy it to an sdcard and stick it into the BlueSCSI, etc..

At one point, I was able to transfer all of the files on several 'drives' on the BlueSCSI to SCSI2SD, when I swapped devices to use internally. But lately, when trying to copy anything, it would inevitably fail! Turning off termination on SCSI2SD has apparently fixed it, as the BlueSCSI terminates the SCSI bus!

I think I had the SCSI2SD externally mounted when this worked originally, now that I look back on it.

Ah SCSI!

 

[Hurry]

That's why I'm confused about the internal physical SCSI HDD + external RaSCSI (terminated with external power supply) not working. I would expect the Mac to see it like any other external SCSI device presuming the termination is present at the end of that particular chain. I know the RaSCSI works, but I haven't used it on THIS machine before, and I realize I don't know if the external SCSI port on this device works. I think I'm going to try and keep it simple and troubleshoot that next. This is one of those odd situations where any combination of Google query turns up a variety of unrelated topics. I will also try hitting up the Open Retro SCSI Discord. If I get it working I'll post here what I find out.

 

[Hurry]

In the FWIW department, I confirmed that the SCSI port is fine on that machine. I took the question to the Open Retro SCSI RaSCSI Discord and the best response I got was "Mac termination is weird". “¯\_(ツ)_/¯

It's annoying as I think about it - this makes RaSCSI basically useless to me. Not interested in the web piece, and not interested in having a second power supply and external box hanging off of the back of my compact Mac. BlueSCSI it is then, once I get a good external SD card mount designed and printed.

 

[mg.man]

this makes RaSCSI basically useless to me

More on the FWIW side, I had the chance recently to 'play' with a RaSCSI, which worked fine on my '030-enhanced SE, but went berzerk on my Plus. I forgot (and didn't get a chance to do the mod) that the Plus lacked TERM PWR, so perhaps that would have helped... I know lots of ppl rave about the RaSCSI, but I prefer something that "just works" without too much faff... Obviously, YMMV!

 

[Hurry]

More on the FWIW side, I had the chance recently to 'play' with a RaSCSI, which worked find on my '030-enhanced SE, but went berzerk on my Plus. I forgot (and didn't get a chance to do the mod) that the Plus lacked TERM PWR, so perhaps that would have helped... I know lots of ppl rave about the RaSCSI, but I prefer something that "just works" without too much faff... Obviously, YMMV!

Now that I think about it I probably should have been more specific. I think the RaSCSI is cool as heck - the ability to drag and drop disk images to my compact mac via a web browser is awesome. I'm sure the networking/web stuff is cool too, that's just too much like "day job" to me and I don't have a lot of utility for that feature. In my situation though, it's not a permanent solution I'm interested in, though. I have limited space and like to be able to swap in and out/grab different machines from a shelf and bring it over to my desk for a while. I really want to be able to do this with as little fuss as possible. For my wants/need, I want to know that I can grab my SE/30, power it up, and go. Maybe if I had a nice permanent "retro battle station" area where I could leave things up and running semi-permanently I'd feel differently.

The trick for me, now that I've described my wish list, is that I'm pretty much sneaker-net for adding software if I use a BlueSCSI - which means I need easy access to remove and replace that SD card. It's no big deal, a MicroSD card extender is cheap - it's just a matter of printing up a bracket of some kind to make it easier.

 

[mg.man]

I'm pretty much sneaker-net for adding software if I use a BlueSCSI

I tend to used my BlueSCSIs as solid state HD replacements. I usually use two partitions, one for System folders (I use a System Folder switcher to move between 6.x and 7.x) then another partition for "stuff". IoW, I rarely (if ever) change the SD card. For moving stuff, I have a variety of external SCSI devises (Zip, CD, HD) that I can plug into. I also have a FloppyEMU - which I can use in HD20 mode - it too has multiple HD images I can choose from.

If you really want easy access to switch the SD card, there is this...

BlueSCSI 1.1a Expansion Slot Bracket for SE and SE/30

Hey 68kMLA! I'm very excited to finally release my latest printed bracket design, which mounts the BlueSCSI 1.1a in the Expansion Slot on a Macintosh SE or SE/30! The main goal of this bracket is to make the microSD card as easily accessible as possible, while keeping your Mac fully...

68kmla.org

I'm also considering setting up a period file server and Local/AppleTalk connection. In your scenario, if you set something up along those lines, you could just have a Local/AppleTalk cable available at your "play" area you can plug whatever machine into. Of course, you could also have the RaSCSI sitting there ready to plug into the SCSI port of whichever Mac you're tinkering with - but then you're back to the BlueSCSI internal vs. RaSCSI external termination tug-o-war...

 

[Hurry]

For moving stuff, I have a variety of external SCSI devises (Zip, CD, HD) that I can plug into. I also have a FloppyEMU - which I can use in HD20 mode - it too has multiple HD images I can choose from.

Yes! I forgot about my FloppyEMU! I think of it as an Apple II device, but I recall it has capability with some firmware touching to work with a Mac.

If you really want easy access to switch the SD card, there is this...

BlueSCSI 1.1a Expansion Slot Bracket for SE and SE/30

Hey 68kMLA! I'm very excited to finally release my latest printed bracket design, which mounts the BlueSCSI 1.1a in the Expansion Slot on a Macintosh SE or SE/30! The main goal of this bracket is to make the microSD card as easily accessible as possible, while keeping your Mac fully...

68kmla.org

Yes (x2)! I was planning to design and print my own - the only other design I saw online seemed janky for what I wanted to do - this is newer and much nicer, thanks again!

I'm also considering setting up a period file server and Local/AppleTalk connection. In your scenario, if you set something up along those lines, you could just have a Local/AppleTalk cable available at your "play" area you can plug whatever machine into. Of course, you could also have the RaSCSI sitting there ready to plug into the SCSI port of whichever Mac you're tinkering with - but then you're back to the BlueSCSI internal vs. RaSCSI external termination tug-o-war...

This is where I start to feel like I'm at work, not at play. If I had more space to operate I might consider this - that "always on when you need it" bridge machine to connect everything. But right now, I don't mind the hassles of not having networking if it keeps me from having to do... networking.

 

[Hurry]

You know how the RaSCSI has the ability to add a second SCSI port for additional devices? I wonder if I turned off termination on the RaSCSI and added a SCSI 1 terminator to that second port if it that would solve the problem? I don't have one to try, but I'll keep an eye out at VCF or order one to find out. Not a useless thing to have in the parts drawer anyway.

 

[luminescentsimian]

an external Active terminator instead of the passive resister nets on the *SCSI emulators would probably work better

 

[mg.man]

Did someone say...

bridge Machine

Here's my does most things setup:

Pumped up with a Sonnet G3/400. Just need to get the Tango FW/USB fully working and I can button it up...

 

[mg.man]

AWESOME!

Thanks! Hoping to make it a little moreso soon... have a XLR8 carrier card with a G4/400 Zif CPU coming my way...

 

[Byte Knight]

an external Active terminator instead of the passive resister nets on the *SCSI emulators would probably work better

I tried this too without any luck. I just picked up the AzulSCSI and it works fine internally with the external RaSCSI...