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I saw JT's mention of the need for this thread here:

 

http://68kmla.org/forums/viewtopic.php?p=163030#p163030

 

so I decided to start rolling that ball. I posted a lot about this topic back in the 90s in the comp.sys.mac.* hierarchy in the news groups, so at first, I'm just going to quote some of my old postings as I find them. After a week of desultory searching in Advanced Google Groups Search, I've found my first useful posting, quoted below Early SCSI History:

 

Alan Lehotsky wrote:

> Can someone concisely explain what the difference is?

> Can I use a drive that supports fast or wide or ultra with

> any old SCSI controller and just not get the maximal performance?

> Or, is it that the interfaces are incompatible?

> -- Al

 

This is probably explained better in the FAQ over on comp.periphs.scsi,

or that might be comp.periph.scsi. But here it goes:

[2012 Edit: comp.periphs.scsi FAQ, Part 1 of 2

[2012 Edit: comp.periphs.scsi FAQ, Part 2 of 2

 

In the beginning there was SCSI and it was pretty good and it maxed out

at transfer rates of about 3 MB/s. But that was the early 80's, so

it was faster than any hard drives worked anyway. There were

ambiguities in the IEEE standard as written, so SCSI from one company

wasn't necessarily compatible with SCSI from another company. This

problem mostly expressed itself in the PC world as little proprietary

SCSI controllers that were included with scanners or other peripherals

and that wouldn't work with any other SCSI devices. We had it good

in the Mac community when it came to SCSI, except that most of Apple's

implementations would do maybe 1.5 MB/s transfer rates.

 

SCSI was based on a 50 wire cable transferring 8 bits of data in

parallel. The other 42 wires are ground wires and various control

signals. The frequency of data over this cable is also part of

the standard but I don't remember the number. I think it was

10 MHz. [2012 Edit: It was 5 MHz.]

 

So it was decided to write a new SCSI standard that would vanquish the

ambiguity and while they were at it, they decided to add some

improvements, because 3 MB/s was getting pokey.

 

Thus was SCSI-2 born. By making use of synchronous transfers (or maybe

that was asynchronous transfer [2012 Edit: It was synchronous],

I get the two confused) SCSI-2 was

able to up the transfer rate to 5 MB/s using the same 8 bit parallelism

at the same frequency as the old SCSI standard. But the standards-makers

were not satisfied. So they added two more options to SCSI. It could

be Fast--operating at twice the normal frequency, and/or it could

be wide--transferring 16 bits of data in parallel instead of 8. And just

to help confuse things, they prescribed a new SCSI connector to replace

teh old Centronics 50--the High Density SCSI connector--often called

a SCSI-2 connector because it came out when the new standard was

written.

 

And the standards-makers declared backward compatibility. The original

SCSI devices would work on the same bus as the SCSI-2 devices. And Fast

SCSI-2 devices would work with them all. But to take advantage of the

new features, both of the devices communicating must have the same

features. What this means in proactice is that the user would never

get performance better than what his SCSI controller supported and the

controller would have to slow down to the speed of whatever device it

was talking with at the moment.

 

Because Wide devices transfer 16 bits at a time, they need a different

cable. You must have some extra wires to carry those 8 extra bits.

So Wide devices usually go on their own 68 wire bus. But those wily

SCSI Standards-writers thought of everything. If you put an

adapter on a wide device and attach it to a narrow bus, or put

an adapter on a narrow device and attach it to a wide bus, the

controller and the device will negotiate their transfer method,

and agree to just use 8 bit transfers, so that you don't have the

other 8 bits getting lost in the ether somewhere.

 

Wide devices usually cost a little extra, so people usually don't

buy them and then handicap them by putting them on a narrow bus.

And putting a narrow device on a wide bus can decrease the overall

performance of the wide bus, as well as causing issues with SCSI

ID's over 7 (wide uses ID's 0-15), so it's best to avoid that too,

if you can.

 

A note--wherever I write "wide" I really mean Fast & Wide. I've

never seen one, but a SCSI drive that was simply Wide, would have

a maximum transfer rate of 10 MB/s, the same as a Fast narrow one.

It's the combination of Fast (twice the bus frequency) with wide

(twice as many bits in parallel on the bus) that gets the

20 MB/s theoretical transfer rate of Fast & Wide.

 

Still later a newer SCSI standard was born and it was called

Ultra-SCSI. I'm less familiar with this new stuff, but somehow

it upped the maximum transfer rate on the old familiar 50 wire

cable to 20 MB/s. Yet, it is backward compatible in the same way

that SCSI-2 and Fast SCSI-2 was. Just keep in mind, that if you

put an Ultra-SCSI drive on a plain SCSI-2 controller, your max performance

will still be 5 MB/s. And any old original SCSI devices on a fancy new

ultra-SCSI chain are still stuck at 3 MB/s. But an Ultra-SCSI

controller with Ultra-SCSI drives can get you 20 MB/s.

 

And following in tradition, there is wide ultra SCSI which does

twice as many bits at the same speed as ultra-SCSI, getting

a maximum theoretical performance of 40 MB/s.

 

So to summarize. There are devices built for 50 wire buses (50 pin

cables) which can all be connected to the same bus without adapters:

 

original SCSI 3 MB/s

SCSI-2 5 MB/s

Fast SCSI-2 10 MB/s

Ultra-SCSI 20 MB/s

 

In general only two devices on a bus talk to each other at any given

time. This is almost always (is always in any case the normal Mac

user will encounter) the controller (logic board or SCSI card) talking

with one of the devices on the chain. These two devices will com-

municate at the rate of the slower device.

 

And there are devices that are built for 68 wire buses:

 

Wide SCSI-2 10 MB/s (never seen one of these, don't think they

were ever built)

Fast & Wide SCSI-2 20 MB/s

Wide Ultra SCSI 40 MB/s

 

Wide devices can be adapted to narrow busses and narrow devices can be

adapted to wide busses, but when you do those devices will only give you

narow performance. And putting narrow devices on a wide bus may slow

down the performance of that bus with the wide devices.

 

Finally there are some 80 pin devices out there, but I'm not sure what

the deal is with them. I think they're built for hot pluggable

systems. And there are what are called Differential drives. These

use a differnet method of interpreting electrical signals as data,

so that they can better tolerate environments with a lot of

electrical noise and use longer cable runs. Differnetial drives

are not compatible with other SCSI drives and can cause damage if

attached to a regualr bus. There are some adapters for differential

drives, but they are so expensive, you are better off just getting

the correct drive in the first place.

 

Hope this helps. It's not concis...oh well.

 

Okay, that's rather incomplete because it's so out of date and not very concise. But I don't have time to write something short and to the point at the moment.

 

Oh, I also found this useful link: http://www.scsifaq.org/

 

I'm still looking for my old postings on configuring SCSI chains properly and the finer points of mixing wide and narrow drives. As I recall, those had some nice ASCII diagrams included.

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Finally found another old message. This one is from the early days of the LEM Lists before they went to Google Groups.

 

=======================================

SCSI Voodoo exists because SCSI works when it shouldn't, not because

it doesn't work when it should. So folks misconfigure their SCSI

chains, the machine works anyway, they think everything is fine, then

one day it stops working and they declare SCSI Voodoo.

 

If your cables are short and your SCSI bus is slow it will still work

without termination, sometimes. The things which termination deal

with are into the realm of analog electronics as opposed to digital

and so it's not an all or nothing deal. Sometimes poor or no

termination is still good enough.

 

A great site: http://www.scsifaq.org .

 

Basic SCSI:

 

1) I will use the terms chain and bus pretty much interchangably.

 

2) Every device on the SCSI bus must have a unique SCSI ID. It

doesn't matter what order the IDs are in, just as long as they are

each unique.

 

3) A "device" is anything on the bus, including the host computer, a

SCSI card, disk drives, scanners, etc.

 

4) No branches are allowed in a SCSI chain, i.e. no Y formations.

 

5) Every SCSI bus/chain has two ends and only two ends. It's a line

because there are no Ys.

 

6) Each end of the SCSI bus must be terminated.

 

7) You, the user, may only need to provide termination at one end,

because some device (host computer, or SCSI card) may be providing

termination automatically for the other end of the chain.

 

8) Here are some example SCSI chains:

 

Key

===== internal SCSI ribbon cable

:T or T: A SCSI terminator or termination on a SCSI Device

Dn A disk device of some type, such as a disk drive, n is an integer

which I'm just using as a label for easy communication. It has

nothing to do with SCSI IDs.

C A connector on a SCSI cable with no device attached

MB The host motherboard, or a SCSI card

-------- external SCSI cable

 

 

Example 1, Internal SCSI only; Good Termination

 

T:MB===D1====C====D2:T

 

The motherboard provides termination at one end and the device at the

end of the chain provides termination at the other end. Notice that

the device providing termination is on the last connector on the

cable.

------------------------------------------------------------------------------------------------------------

 

Example 2, Internal SCSI only; Bad Termination

 

T:MB===D1====D2:T====C

 

The motherboard is still good, but now the terminating device at the

other end of the chain is no longer at the end of the cable. Unless

the distance from D:T to C is only a few inches this is a SCSI no-no.

------------------------------------------------------------------------------------------------------------

 

Example 3, Internal SCSI only; Bad Termination

 

T:MB===D1:T====C====D2

 

The motherboard is still good, but the second terminating device is

not at the end of the cable where it belongs. D1 should have

termination disabled and D2 should have it enabled, or their

positions on the cable could be reversed.

------------------------------------------------------------------------------------------------------------

 

Example 3a, Internal SCSI only; Bad Termination

 

T:MB===D1====C====D2

 

The motherboard is still good, but there is simply no termination for

the other end of the chain. This is bad as both ends of the bus

must be terminated.

------------------------------------------------------------------------------------------------------------

 

Example 4, External SCSI only; Good Termination

 

T:D2----D1------D3------MB:T

 

Note that this looks pretty much exactly like good internal

termination. The biggest difference to note is that with external

devices one usually leaves the on-board (built-in) termination turned

off and uses an external terminator module. The module plugs into

the unused cable connector at the end of the SCSI chain. Every

external SCSI device should have two SCSI connectors. One for each

of the two external cables that connects it to the neighboring

devices. When you reach the end of the chain, there's only the one

incoming cable, so the other cable connector is available for a

terminator module to plug into.

 

Also note that if you use an external module, it is very difficult to

incorrectly terminate your external SCSI chain. You can only plug

the terminator into the last device on the chain, becuase it's the

only one with an empty cable connector. However, you can still

screw up by enabling termination on one of the intermediate devices

on the chain.

 

Some external devices have only one SCSI connector and have

termination permanently enabled. Such devices must go at the end of

the SCSI cable.

------------------------------------------------------------------------------------------------------------

 

Example 5, External SCSI only; Bad Termination

 

T:D2----D1:T------D3------MB:T

 

In this case SCSI device D1 somehow has termination enabled. It is

not at the end of the SCSI chain so this is wrong. There are two

primary ways this could happen. D1 could be a disk drive of some

sort and the user left the "Termination Enable" jumper installed so

that D1's built-in termination is still enabled. Or the case in

which D1 is installed may have a built-in termination feature and it

may be switched on. Some of the APS brand cases came with this

termination feature.

 

So, when you put SCSI devices on an external SCSI chain be sure to

disable the built-in termination (remove the SCSI Term Enable

jumper), unless you will not be using an external terminator, and the

device will be at the end of the chain. But using the built-in

termination is a bad practice because you cannot see at a glance

whether termination is enabled on a device. And you would have to

pull the device out of its case to check the jumpers.

------------------------------------------------------------------------------------------------------------

 

Example 6, External SCSI only; Bad Termination

 

T:D2:T----D1------D3------MB:T

 

This example builds on the information in example 5. The last

device on the chain is terminated but it is double terminated. This

happens when the user leaves the "Termination Enable" jumper

installed on the SCSI device and installs an external termination

module on the unused cable connector on the last device. This is

also a big no-no.

------------------------------------------------------------------------------------------------------------

 

Example 7, External SCSI only; Bad Termination

 

D2----D1------D3------MB:T

 

This one is trivial. There is no termination at the left end of the

SCSI chain. Termination needs to be provided in some manner.

------------------------------------------------------------------------------------------------------------

 

Example 8, Internal & External SCSI; Good Termination

 

T:D2----D1------D3------MB===D5====C====D4:T

 

Most Macs which shipped with built-in SCSI have both an internal and

an external SCSI connector and these connectors are both on the same

SCSI bus. In a PCI Mac such as the x500 and x600 series which have

two SCSI busses, this internal/external SCSI bus shows up as Bus 1 in

utilities such as SCSIProbe.

 

So, in this case we have devices on both the internal connector and

the external connector. This involves two different types of

cabling: a ribbon cable on teh inside and external cable in a chain

of cables and boxes on the outside. However, it is still a straight

line. The rules still apply. There must be a terminator at each

end of the chain.

 

So the last device on the ribbon cable must be at the end of the

ribbon cable and it must have termination enabled (usually the

"Termination Enable" jumper installed). The last device on the

external chain must have a terminator installed.

 

The motherboard detects that it is no longer at the end of the SCSI

chain and automatically disables its built-in termination. This is

documented in the Apple Developer Notes for these machines.

------------------------------------------------------------------------------------------------------------

 

I'm going to skip the "Bad Termination" examples for internal &

external because they can be drawn from teh examples for internal

only and external only.

 

Mac models such as the x500 and x600 machines and the 8100 have two

built-in SCSI busses. Each bus must be properly terminated. So an

example would be:

 

SCSI Bus 0 T:MB===D====C====D:T

SCSI Bus 1 T:D----D------D------MB===D====C====D:T

 

The machines with two built-in SCSI busses have two internal SCSI

connectors. One of those connectors is the sole connector for SCSI

Bus 0. The other connector is the internal connector for SCSI Bus 1

and is on the same SCSI bus as the external SCSI connector.

 

I think that's enough. There's a bunch I could write on SCSI IDs

and SCSI cards, but there's a length limit on messages to the list.

 

Jeff Walther

=========================================================

 

Still looking for one of my old messages, with similar examples and diagrams about mixing narrow and wide devices...

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Another old message.

 

=================================================

...

Now on to our regularly scheduled pedantry... Single ended simply means that it is not differential. It refers to the form of the electrical signals sent over the cables and is not descriptive of the wires or cabling.

 

In the beginning there was single ended SCSI and differential SCSI and only very high end installations used differential so all you needed to know was to avoid differential stuff.

 

Now days, we have the wonderful LVD which is Low Voltage Differential. U2W SCSI and the later versions (U160, U320) are LVD. Most, if not all, of the U2W drives are capable of operating in Single Ended mode, which means that they adjust their form of electrical signaling to the old style if they find themselves on a SCSI bus where that is what is being used.

[2012 Edit: One big advantage of LVD signalling and cabling is that the cables can be longer than what was allowed for UW, the previous generation of SCSI.]

 

SCSI termination and cabling for LVD is quite different from single ended though they appear similar. The single ended 68 pin cable is a just a smooth ribbon cable. The 68 pin LVD cable is that weird looking twisty turny stuff where the pairs are broken out of the ribbon and twisted around each other.

 

The terminators for single ended (SE) and LVD are also different. However, there's a detail. Most of the LVD terminators will also automagically do SE termination. But the reverse is not true. So, if you get an LVD terminator, you're probably okay, no matter which regime you're operating in, but with an SE terminator, you can only use it on an SE bus. Usually the LVD terminators will have "LVD/SE" embossed on their plastic indicating their dual nature.

 

Similarly, the LVD cabling seems to work fine on SE busses, but don't try the reverse.

 

If you're running an SE bus (UW or earlier) then it doesn't matter much which form of cabling you choose. But these days, if you're buying new, you may as well pick up the LVD cabling and termination.

 

Also note that most U2W and later drives do not have an option to enable on-board termination. They depend on there being a separate terminator installed on the SCSI cable. UW drives and earlier have a jumper which will enable termination on the drive, so that the drive can go at the end of the SCSI cable instead of a termination module. This means that you generally need one more position (plug) on an LVD SCSI cable than you would have needed on an SE SCSI cable.

 

Jeff Walther

========================================================

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  • 9 months later...

SCSI Termination Resistor Packs:

 

These are SIP (Single Inline Pin) assemblies with internal arrays of resistors used to provide termination on very old SCSI hard drive and on the FWB NuBus JackHammer card.

 

Insert the resistor packs to enable SCSI termination on the device. Remove the resistor packs to remove SCSI termination from the device.

 

If the termination resistor packs were removed from your device a long time ago, they can be very difficult to replace. Searches on useful terms like "SCSI Termination Resistor Packs" will turn up very little useful information and it will appear that these useful little SIPs are no long available for purchase anywhere.

 

However, if you know that an 8 pin (3 required) SCSI termination pack is a Bourns 4308-104-221/331 or 4608-104-221/331 and search on that, you'll find that several electronics supply houses, such as Mouser, Jameco and Questcomp stock them. For the 10 or 11 pin (2 required) SCSI termination pack use Bourns 4311-104-221/331. Or if it's 10 pin then 4310-104-221/331.

 

I found that at Mouser there are extra letters in the full part number, so a search on 221/331 is more useful.

 

If you can't find the 43xx then search for the 46xx. The only difference is the package above the pins.

 

http://www.mouser.com/ProductDetail/Bourns/4610X-104-221-331L/?qs=sGAEpiMZZMvrmc6UYKmaNccpGBHYJbrG99AJVMM%252bfMk%3d

 

http://www.mouser.com/ProductDetail/Bourns/4608X-104-221-331LF/?qs=sGAEpiMZZMvrmc6UYKmaNdB1hNUXmH4oGn7oAwLmg%252bM%3d

 

Jameco:

http://www.jameco.com/webapp/wcs/stores/servlet/StoreCatalogDrillDownView?langId=-1&storeId=10001&catalogId=10001&position=1&refineType=1&sub_attr_name=Circuit%20Designator&refineValue=TERM&refine=1&history=eu0ex3tu%7CfreeText~bourns%5Esearch_type~jamecoall%5EprodPage~15%5Epage~SEARCH%252BNAV%40q42xnljl%7Ccategory~205031%5EcategoryName~cat_2050%5Eposition~1%5Erefine~1%5EsubCategoryName~Passive%2BComponents%2B%252F%2BResistors%2B%252F%2BNetwork%252C%2BSIP%5EprodPage~15%5Epage~SEARCH%252BNAV%40vzyb4mar%7Cposition~16%5Erf~1%5Erefine~1%5EprodPage~15%5Epage~SEARCH%252BNAV

 

 

http://www.bourns.com/pdfs/scsitermap.pdf

 

http://www.bourns.com/data/global/pdfs/4300R.pdf

 

http://www.bourns.com/data/global/pdfs/4600H.pdf

 

http://www.bourns.com/data/global/pdfs/dutermap.pdf

 

http://www.bourns.com/data/global/pdfs/bourns_networks_short_form.pdf

 

http://www.bourns.com/data/global/pdfs/Bourns_N1065_4600_Alternative_FPB.pdf

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  • 1 month later...

In the SCSI chain, bandwidth is SHARED. If you have 7 hard drives in the SCSI chain and they are all going at the same time they get 1/7th of the bandwith.

 

If there is just one hard drive in the chain that is active it gets all of the bandwidth. With tape drives, ZIP dridve, and CD-ROMs thrown in, who knows how much bandwidth a device will get.

 

Vendors like to publish data on their device with it being the ONLY device in the chain.

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  • 2 weeks later...

It depends on what you mean by "shared".

 

Only two devices can communicate at a time on a SCSI bus. So at any given moment, the bandwidth is not shared. It is all devoted to the channel between the two devices (usually the host controller and a device) which are currently communicating.

 

Further, SCSI devices have a priority ranking based on their SCSI ID, which determines which devices get control of the bus, if multiple devices are trying to talk at the same time.

 

SCSI ID 7, usually the host controller, always has the highest priority. From there, highest priority is ID 6 and descends to 0. If the SCSI bus is a wide bus with IDs from 0 - 15, then the previous statement is still true, but after SCSI ID 0, ID15 has the next priority and descending from 15 to 8.

 

Of course, if you have an array of disks, all on the same SCSI bus, and a controller scheme which gives them all about equal usage, then it will look a lot like the bus is dividing its bandwidth evenly amongst them all.

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  • 5 years later...

trag, I have a Quantum LPS 540S SCSI drive that's missing its two 10-pin-each terminator SIPs at RP1 and RP2 (see photo below).  I went through the links in your earlier post and found the BOURNS 4610X-104-221/331L at Mouser.  Can you confirm if that is indeed the correct part number for use in my particular Quantum drive?  Thanks.

 

QuantumLPS_540S_TerminatorsMissing.thumb.jpg.4efb96fcca001dfa2645a0717b331212.jpg

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On 11/14/2018 at 4:02 AM, JDW said:

trag, I have a Quantum LPS 540S SCSI drive that's missing its two 10-pin-each terminator SIPs at RP1 and RP2 (see photo below).  I went through the links in your earlier post and found the BOURNS 4610X-104-221/331L at Mouser.  Can you confirm if that is indeed the correct part number for use in my particular Quantum drive?  Thanks.

 

That should be the thing.   It's possible that I went down a rabbit hole and didn't know it, but I don't think so.  Proper SCSI terminators connect each terminal to ground through a 220 0r 330 ohm resistor and the same terminal to 5V through the other resistor value (don't remember which is which).   And looking at https://www.bourns.com/data/global/pdfs/4600H.pdf    that's what that part does.

 

For added confirmation you might confirm that the first and last terminal for each resistor pack connects to either GND or 5V and that none of the intervening terminals do.   Oh, they (intervening terminals) will probably have connectivity with some resistance, but they won't connect with near zero resistance.

 

 

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Simple enough to check.   Just check continuity on the pins at the ends of the two connectors.   Again, a connector that expects the 330/220 style will have 5V at one end and GND at the other end.  Should be able to use the power connector for the other end of hte test, most likely, unless they put a voltage regulator in between.

 

The configuration you show in the picture would just have GND, probably, at Pin 1.  The other nine pins would be connected to SCSI signals.

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Trag,

 

Doing a continuity check with my Fluke 8845A benchtop meter yields no continuity at all between the leftmost and rightmost pins of RP1 and RP2 (see my photo above).  The same is true when checking continuity between all the other pins of RP1 and RP2.

 

Checking resistance using my Fluke between the leftmost and rightmost pins of RP1 shows 11k-ohm.  Probing between the leftmost pin and all other pins of RP1, except for the rightmost pins also yields 11k-ohm.  Measuring between the rightmost pin of RP1 and all other pins, except the leftmost pin, shows 9k-ohms.  I then repeated for RP2 and got the same resistance measurements.

 

I also took voltage measurements using my Fluke.  I get +2.78V with my (+)RED probe on RP1's leftmost pin (see my photo above), which is silkscreened with a square and has an arrow pointing at it (I guess that is "pin-1"), and my (-)GND probe was on the rightmost pin which has "U12" silkscreened above it.  I then repeated the voltage measurement for RP2 and got the same voltage of +2.78V.  When putting my (-)GND probe on the black wire from the power connector (just a different ground), I get +2.84V.  Putting my (-)GND probe on the leftmost pin and (+)RED probe on the rightmost pin yields -2.78V for RP1 and RP1, which confirms that the leftmost pin is indeed POSITIVE.  Even so, this voltage is not the 5V you mentioned it should be.

 

For your reference, voltage measured at the floppy connector measures 4.8V with my SEASONIC PSU inside.  My motherboard is recapped but the analog board is not.

 

Any further thoughts you may have would be greatly appreciated.

 

Thanks.

 

 

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It sounds like they may have used those 110 ohm SIPPs you referenced above and just tied the signals directly to ~3 V.   It is good that you double checked.   

 

==============================================

Later Edit:  And now that you've set me off...  Found this document.  See page 2.   It describes the style of termination that your drive must be using.  Page 1 describes the original 330/220 style.     Everywhere I wrote ~3V in this message, change it to 2.85V.  :-)  https://www.analog.com/media/en/reference-design-documentation/design-notes/dn034f.pdf

===============================================

 

I just reread  http://www.bourns.com/pdfs/scsitermap.pdf  referenced several messages above and it states that there are 18 signals to terminate.    Three eight-pin SIPPs of the 330/220 variety would provide that, because they lose one pin each to 5V and GND, leaving six signal pins on each SIPP.   Three times six is then eighteen.

 

However, two ten pin SIPPs just can't terminate eighteen signals using 330/220 SIPPs.   There are only 8 signals lines per SIPP, yielding 16 signal lines.

 

Two 11 pin SIPPs could terminate eighteen signals using 330/220 SIPPs, but that's not what we've got here.

 

So, my best guess is that pin one of your RP1 and RP2 are a regulated ~3V.   All the other pins are signal pins and when the SIPP is installed are tied through a 110 ohm resistor to pin 1, giving you 9 signal pins per SIPP and yielding the full 18 signals.

 

In this case you want the 101 circuit (See Figure labeled "Bussed Resistors (101 Circuit)" on page 2 of https://www.bourns.com/data/global/pdfs/4600H.pdf). 

 

You will want the 110 ohm version.  The part number should be something like 4600H-101-111  or in more modern terms, something like this:  https://www.mouser.com/ProductDetail/Bourns/4610X-101-111LF?qs=sGAEpiMZZMvrmc6UYKmaNfXDPPK60BkBqMgbUjJrIUk%3d

 

Actually, any of these should work:    https://www.mouser.com/Passive-Components/Resistors/Resistor-Networks-Arrays/_/N-e89l?P=1z0wo93&Keyword=bourns+101-111&FS=True

 

If you really want to be certain, get a copy of the pinout for the 50 pin SCSI connector.   Identify the 8 data lines, 1 parity line, and 9 control lines.    Check that each of those eighteen lines has unique continuity with one of the pins in RP1 or RP2 and none of them connect to Pin 1 of RP1 or RP2.

 

That would make it certain that when using the 101 style SIPPs each signal is simply being connected through 110 ohms to a ~3V source.

 

For Future Reference:   Given that 18 signals must be terminated:

 

1)  If your hard drive uses three 8 pin SIPPs, then it is probably using the 104 circuit, 330/220 style SIPPs.

2)  If your hard drive uses two 10 pin SIPPs then it is probably using the 101 circuit 110 ohm (?) style SIPP.    (still a little uncertain about what resistance the SIPP should be and what voltage pin 1 should be regulated to).  

3)   IF your hard drive uses two 11 pin SIPPs then it is probably using the 104 circuit 330/220 style SIPPs.

 

Guide to part numbers for the above situations are in  https://www.bourns.com/data/global/pdfs/4600H.pdf

 

 

In all three cases go to https://www.mouser.com/Passive-Components/Resistors/Resistor-Networks-Arrays/_/N-e89l/

 

1 & 3)   Search on "Bourns 104-221/331"

Then select "220 ohms, 330 ohms" in the "Resistor Values" field.,   For Case 1, select "8" and for Case 3 select "11" in the "Number of Pins" field and click on "Apply Filters".

 

2)   From the link above, search on "Bourns 101-111".    Select "10" in the "Number of Pins" field and click on "Apply Filters".

 

 

Moderators:   Is it possible to change my May 8th 2013 message.     This part is wrong, " For the 10 or 11 pin (2 required) SCSI termination pack use Bourns 4311-104-221/331. Or if it's 10 pin then 4310-104-221/331. "  

 

Maybe insert a note that if your hard drive uses 10 pin SIPPs look down to this message.

Edited by trag
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My humble thanks to Trag and joethezombie for sharing such helpful information.  

 

Just as I began writing this reply, I decided to spend an hour looking through my box of old vintage Mac "small parts" and sure enough I find an old 10-pin SIP that I remember removing from one of my Quantum drives many years ago. A photo of that 10-pin SIP is below.  I believe the reason I don't still have the second SIP is because when I removed it, it broke apart, so I probably disposed of it.  The printing on the SIP is "T10-1-111F 420." I took my DMM and measured voltage between the leftmost (pin1) and the rightmost pin found it to be 110-ohms.  I got the same reading between pin-1 and the other pins.  And between any two pins (excluding pin 1) I get 220-ohms.  So this confirms what joethezombie said, and confirms what Trag said about the BOURNS 4610X-101-111LF being the correct replacement 10-pin SIP (and remember that you'll need two of them.  I also found an old Apple branded 160MB Quantum drive that looks exactly the same as the photo I posted previously of my 540S, and it too is missing it's SIP terminator pair.  The same kind of SIP would most likely work perfectly in it as well.

 

By the way, I have an Apple HD20SC zero-footprint drive enclosure with a SCSI HDD inside that is terminated via jumper.  When I connect my SE/30 (which has my unterminated Quantum LPS 540S inside) to that HD20SC, even if the power is OFF on the HD20SC, the SE/30's internal Quantum drive will boot.  So the termination on the external drive allows the internet drive to function properly.  I still want to terminate the internal drive though so I can use the machine with that drive even when it's not connected to the HD20SC.

 

Thanks again and hope this discussion helps others who have the same problem!

 

IMG_1347.thumb.JPG.d4ca90ecb46676562e377e1f52bbb8dd.JPG

 

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  • 3 weeks later...

I don't know if this is bad termination, but it was the only way I could get my computer to boot with all my devices attached:

 

SCSI BUS 0 - MB --- HDD --- JAZ --- CDR --- MO1 --- PT:MO2:AT

 

HDD: ID0

JAZ: ID2

CDR: ID3

MO1: ID4

MO2: ID5

 

I left 1 open for a second HDD or Apple brand CD-ROM.

 

If I don't have the passive terminator (with the pass-through connector), even though I have the end of the SCSI chain terminated, it still fails.  I also tried switching around the order of the devices, but that didn't help.  It also fails if I have just a passive terminator at the end.  For some reason, this combination works.  If I don't have it, then it won't detect one or more of my devices (including the HDD itself.)

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  • 1 year later...

I have the same quantum 540S a mentioned above (a Quantum ProDrive LDS to be precise). What kind of jumpers should I use to assign the SCSI ID? Regular jumpers would be too tall for these pins. Also, an ID diagram would be helpful if anyone has one...

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