SCSI bus termination

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I am trying to connect an old SCSI scanner bought on eBay to a Windows PC for a friend.

She has bought and installed an Adaptec SCSI card and this seems to be recognised by the PC. However although the scanner powers up it is not recognised as a SCSI device. I suspect bus termination issues.

Now I have played with SCSI devices in the past but this has always been at work, where you open a big drawer or cupboard and a load of different cables and terminators fall out and you try a few until it works. There is also usually at least one other SCSI device floating around for you to test with.

I havve a few cables to work with, and something (double ended) labelled as a passive terminator (but not like the terminators I am used to which are usually a single ended plug). Now SCSI bits aren't that cheap, so I don't fancy buying a selection of terminators. Is there any simple DIY way to check out if the bus is O.K. and the terminator is O.K. such as measuring voltages?

Cheers

Dave R

Reply to
David WE Roberts
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*sucks teeth*

Or cabling. The usual flaw there is to use a Centronics printer cable rather than a SCSI cable, but that requires a PC end that looks like a parallel port and a device end that looks like a printer port so hopefully isn't the case here... Best thing is that doing this nearly works! But not quite.

Never seen one of those double ended ones, seems a bit odd.

You should only need one. The scanner will have a pair of SCSI sockets, yes? One terminator to fit on the second socket, one SCSI cable to go from the Adaptec to the scanner.

Check on the scanner, there may be dip switches to enable termination directly. Then all you need to worry about is which SCSI port on the scanner to cable to.

I sent all my big drawer of SCSI bits to ebay a year or two ago, or I'd post you some bits....

Not really, you're stuck with the full-on sacrifice of a chicken - or a bag of turkey twizzlers if that's outside your budget...

Cheers - Jaimie

Reply to
Jaimie Vandenbergh

What sort of SCSI for starters? i.e. what connectors are on the scanner

- the older centronics style 50 way connectors, or the high density SCSI II style, or the (spit) cheap'n'crappy 25 way D connector?

What make and model of scanner, and which Adaptec card?

Check to see if the device has the option of internal termination. Usually a switch (may be a DIP switch) to change. Sometimes on old kit a SIL resistor pack or two to insert/remove.

Reply to
John Rumm

...snip...

FWIW, I have a SCSI scanner but I've always used an active terminator. As others have asked, what make and model scanner?

Paul DS.

Reply to
Paul D Smith

Not all SCSI is the same. What model card is it? By the connector on the card it should have either 'SE', 'LVD' or 'HVD' stamped on it, or a symbol which looks like a > or similar. Let us know what symbol it has if no letters.

SE = 'Single Ended' LVD = 'Low Voltage Differential' HVD = 'High Voltage Differential'

Generally, SE and LVD is compatible, as long as the cable length is short. The devices will communicate at the lower (SE) speed if you have a mix. LVD and HVD are NOT compatible.

I think most scanners will be 'SE', therefore will need an 'SE' or 'LVD' card.

The Adaptec 2940 was available in SE and LVD from memory. The 2944 is HVD and unlikely to be compatible with a scanner.

Active terminators can usually be used with either LVD or HVD. Passive terminators NEED to be the right type for the SCSI bus in use.

Alan.

Reply to
Alan Deane

Heidelberg Linoscan 1400 Scanner. Can't find the details of the SCSI card - will check. The cables and terminator came with the scanner - previously used with Apple hardware, I believe.

I am arranging to get hold of the bits so I can have an extended play. The connectors between card and scanner are D type (68 pin rings a bell) and the terminator is markes Passive (which may not be a good sign) and in IIRC Centronics style. This needs a short adapter cable to connect to the other SCSI port on the scanner which is not a 68 pin D type. Just Googling now suggests that I may need an active terminator.

Will have more information once I get my grubby hands on the kit.

Cheers

Dave R

Reply to
David WE Roberts

Yes, I think we need to know that first... I've seen all manner of different Adaptec boards and SCSI scanners over the years, and trying to determine cabling / termination / SCSI BIOS options is perhaps a bit pointless without knowing the OP's actual hardware.

Broadly-speaking though, you need termination *once only* at *both* ends of the SCSI bus, whether that be done via external terminators (either active or passive) or by the scanner and Adaptec card (or some combination thereof). The scanner's likely a narrow SCSI device; if the Adaptec card is a wide adapter then care needs to be taken to ensure that the high-side of the wide bus is terminated. Something also needs to supply termination power to the bus - the Adaptec card can almost certainly do it, and the scanner may be able to as well. The scanner needs to be set to a different SCSI device ID than the Adaptec card.

Is it labeled as SCSI or has the SCSI logo on it? If not, I suspect that's not SCSI, and plugging it into a SCSI bus might be a bad idea.

Depending on what connectors it has though, there's a chance that it's wide SCSI on one side passing through to narrow SCSI on the other, while terminating the high-side of the wide bus - but I don't recall ever seeing a passive terminator for wide SCSI, only active ones.

cheers

Jules

Reply to
Jules Richardson

Check what SCSI device ID the scanner is set to; in the SCSI world it was typical to have the *controller* set to ID 7, but I have a feeling Apple were different and sometimes (often / always, even?) set their controller to ID 6 - which means there's a chance your scanner's set to 7 and is conflicting with the PC's controller.

If they're 68 pin then it's a wide bus; you need to make sure[1] that the high side of the bus is terminated as the scanner's likely a 50 pin narrow device and will only be able (either by itself or by a terminator connected to its narrow pass-through port) to terminate the low side of the bus.

[1] the cable you have might do it, or that might be why you have that weird terminator with the two connectors, or on many Adaptec cards it's a BIOS option to terminate just the high side of the external wide bus.

Heck, there's even a wikipedia entry for it:

formatting link
Just Googling now suggests that I may need an active terminator. I think you'll probably be OK with passive terminators - the scanner's not particularly high-speed (compared to say, a hard disk), and it's the only thing on the bus (other than the Adaptec itself), and you'll be connecting it all with a shielded cable (things can be a bit more picky when it comes to ribbon cable internal to a machine).

Even with the cabling and termination less than perfect, I think there's a fair chance it should still respond to device identify at startup (even if it subsequently proved flakey during use), so I think you've got some more fundamental problem at play (hardware fault, cable fault, configuration setting etc.)

cheers

Jules

Reply to
Jules Richardson

I can say that the SCSI ID doesn't clash with the controller - first thing I checked.

I may have mis-spoken about the number of pins. The SCSI card has the same number of pins on the D connector as the scanner, so it is probably 50. Can't find the email trail where I sorted this out.

Should be getting all the bits next Monday so I'll be able to supply more info then.

Thanks to all for the help so far.

Cheers

Dave R

Reply to
David WE Roberts

It is official - I am a complete dip switch.

Reset the SCSI ID from 9 to 2 and it all sprang to life immediately.

Thinking about it, I am not absolutely sure why it wouldn't work before. My first reaction (after seeing the SCSI card software scan for IDs 0-15) was that if it was working on a 3 bit address it would have the range 0-7 or

4 bit 0-15 so putting the address below 7 would put it in a valid range for a 3 bit address. This is standard for 8 bit (narrow)SCSI. This seemed to work. But in that case why have a dip switch with values 0 through 9? Cheap implementation of a single dip switch which covers 10 of the 16 values in a 4 bit address? Cheap part which can be set from 0-9 but shouldn't be set above 6? Doesn't seem rational on a semi-professional scanner which cost £1k when you could go round the world on the Queen Mary for 2/6p and still have change for the cab.

Anyway, pleased (and relieved) that it is working. My friend is really chuffed because the test scan of a colour slide was very good quality, and she got a semi-professional scanner for £10 plus the cost of the SCSI card. She will also have to cough for the VueScan software but that looks to be money well spent as the test version drives the scanner really well and nobody else seems to do Windows drivers for it. At some point I may have a play under Linux but the Windows solution fits in with her other software and all in all she has a really good scanner for not a lot of money.

Oh, and I tried it without the terminator (just to see) and the SCSI software reported "insufficient termination" which showed that the terminator was doing something.

The card was (IIRC) an Adaptec 29160N with a 50 way D type connector externally. Termination of the card end of the bus is handled automagically. The scanner had a matching 50 way Centronics style SCSI port, plus another

25 way D type (which was used to terminate with a short 25 way Centronics style cable plus a gender bender passive centronics style terminator) which also suggests 8 bit SCSI (see above). So the final puzzling part is that it had one connector which could connect to Wide, but the other connector for Narrow. Then again SCSI I supports 25 pin D-sub and 50 pin Centronics so this points to a SCSI I device. So I say again why the 0-9 ID dip switch?

Just annoyed with myself that it took so long to fix a trivial error/misconfiguration.

Cheers

Dave R

Reply to
David WE Roberts

If you had it on an external narrow bus (i.e. 50 way connector) then it would not have seen the right address even when the host was polling the higher numbers.

Count yourself you lucky you did not need to do it in binary ;-)

Yup... either a hex thumbwheel type or a row of DIL switches to enter the address in binary seem more common.

You may find Silverfast do a version (at a price!)

Which is a more informative error than you often get ;-)

There are a few versions of that IIRC... (have got the LVD version in one machine, and the older 80Mbit/byte version in this one)

16 bit would quite often use a 68 or 80 way connector IIRC...

I recall spending hours once getting some trivial data link working... caused in the end by whoever made the kit applying the label for the dip switches round the wrong way on the box!

Reply to
John Rumm

Am I the only one who whiled away an idle moment or two by teaching the kids to count in binary on their fingers? I'm losing a bit of flexibility now but I can still represent quite high numbers:-) However decimal 4 and 6 can be misconstrued when rendered in binary when counting from the thumb. One is a very positive number :-)

Reply to
David WE Roberts

No.

Eighteen is significant to some people.

Reply to
Jon Fairbairn

My daughter could count in binary at about 6yo. She refuses to do hexadecimal though. I did get her doing base 3 using half fingers.

two thumbs and an index finger?

Reply to
dennis

Rock and roll!! :-))

Reply to
David WE Roberts

Sorry, Dennis. Failed binary 101

18 = 16 + 2 Which is two fingers. Starting from the thumb (1) Raise Index finger (2) Raise little finger (16) Rabbit ears, devils horns, whatever.
Reply to
David WE Roberts

Ah, why start with the thumb?

I start from the little finger as it avoids the 6yo making rude signs she doesn't know about.

Reply to
dennis

Still only two digits raised.

Reply to
David WE Roberts

So you don't have a missing thumb?

Reply to
dennis

well its not opposed, if that's what you mean..

Reply to
The Natural Philosopher

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