Strange SCSI behaviour - maybe missing terminator?!?

[mechy]

Yes, that was my point; it can't write last anything to a CDROM so it just keeps checking all the IDs and LUNs.

Any help with the rest of the post on how active termination circuits work without power?

i guess i misunderstood what you were saying about the cdrom.

on the terminators, Someone else answered that for you earlier(Zac iirc), but the answer is they dont,you always need term power or terminators do not work

most active terminators use a custom chip to keep bus levels right,it of course also needs power.


Mike

[danbeaver]

Active termination has nothing to do with term power.
mech

 Herein lies my problem, if the active termination circuits don't have anything to do with the "term[ination] power" then what or where comes the power used to keep them, well, "active?"

[JohnFante]

As far I can see there are two causes of the problem:

There is some kind of conflict between my Plextor CD-Rom drives and the rest. Probably a dodgy terminator.

I lack terminator power. And I think this is the real culprit.

My two HD's have SCSI-ID 0 and 1. I have set the ID for the CD-drive to 2, turned on parity, turned of termination. See the attached photo for a detailed layout of the jumpers.

Both drives (I have tried them individually) show the same error. When I try to boot my drives dosn't spin up and I go directly to the Kickstart 3.1 bootmenu.

The Seagate HD (wich has ID 0 and is first in the chain) has a jumper for termination power. At the moment it is off.

The IBM HD (which has ID 1 and is the second in the chain) dos not have the ability to supply termination power. Only the 68SE model has that and mine is not that. It connects through a rather strange interface. Se photo.

Can I enable termination power on the first drive (Seagate) without risking to cause damage? Or do I have to move it to the last place before the terminator?

If I do not move it the chain would then be:

Active terminator
CSPPC
Seagate HD (with termination power enabled)
IBM HD
CD-ROM
Active terminator

Thank you in advance.

[Zac67]

The pic on the right is an SCA adapter. SCA is an interface intended for connecting into a backplane, there's no termination or termpower provided (there are some SCA adapters with terminators but this isn't one).

Termpower is often provided by several devices but I've had - rare - occasions when that was a problem somehow (which I can't explain I'm afraid). Best practice is to provide termpower by the host adapter and if that isn't possible from the devices at the end of the bus, near the terminators. Terminators with an LED have the advantage of showing you whether termpower's present.

SCSI IDs: the RDB 'last drive' option just stops scanning further drives for RDB automount purposes, so it's perfectly reasonable to put an optical drive on higher IDs. I'm running my boot drive on ID1, so I can add a temporary drive at ID0 without having to fiddle with HDToolBox. Opticals (if present) are on 4 & 5, a tape on 3. 6 I reserve for a 2nd host adapter (PC side) but I haven't 'SCSI-netted' for ages.

[psxphill]

Herein lies my problem, if the active termination circuits don't have anything to do with the "term[ination] power" then what or where comes the power used to keep them, well, "active?"

both active and passive terminators use term power.
 
Passive terminators are a bunch of resistors from the bus lines to term power.
 
Active terminators are similar, but as well as pull up resistors they have voltage regulators.
 
Wikipedia has a bit more detail
 
Parallel SCSI buses must always be terminated at both ends to ensure reliable operation. Without termination, data transitions would reflect back from the ends of the bus causing pulse distortion and potential data loss.
A positive DC termination voltage is provided by one or more devices on the bus, typically the initiator(s). This positive voltage is called TERMPOWER and is usually around +4.3 volts. TERMPOWER is normally generated by a diode connection to +5.0 volts. This is called a diode-OR circuit, designed to prevent backflow of current to the supplying device. A device that supplies TERMPOWER must be able to provide up to 900 mA (single-ended SCSI) or 600 mA (differential SCSI).
 
Some early disk drives included internal terminators, but most modern disk-drives do not provide termination which is then deemed to be external.
 
Termination can be passive or active. Passive termination means that each signal line is terminated by two resistors, 220 Ω to TERMPOWER and 330 Ω to ground. Active termination means that there is a small voltage regulator which provides a +3.3 V supply. Each signal line is then terminated by a 110 Ω resistor to the +3.3 V supply. Active termination provides a better impedance match than passive termination because most flat ribbon cables have a characteristic impedance of approximately 110 Ω. Forced perfect termination (FPT) is similar to active termination, but with added diode clamp circuits which absorb any residual voltage overshoot or undershoot.
 
 
No term power, no termination. I doubt you can cause damage from enabling term power on any of the devices, no matter where they are on the bus. The only problem I could imagine would be a voltage drop, but the regulator in an active terminator will sort that out.

[JohnFante]

Well I moved the HD's so that the chain is as follows:

Active terminator
CSPPC
IBM ID0 - no term power
Seagate ID1 - term power
CD-ROM ID2 - no term power
Active terminator

When I have that chain I still go to the kickstart 3.1 boot menu.

When I remove the CD-ROM it boots into OS4.1 fine (placed on the IBM).

I most admit I am loosing hope here. Once during my fideling around I got the CD to work. Then I put all hardware in its places and changed som ID jumpers and then it didn't work again. Do not know why? :-(

I have an old IDE DVD-drive laying around. Can I use that on the IDE channel? I know it is not that fast but since I am will not be using it for anything but installation that would be just fine.

SCSI kind a suck right now ....

[mechy]

Herein lies my problem, if the active termination circuits don't have anything to do with the "term[ination] power" then what or where comes the power used to keep them, well, "active?"

i think you misunderstood what i meant  i was saying they are 2 seperate things. some people comfuse term power as termination etc.
Some people don't realize what term power was for.

mech

[mechy]

Well I moved the HD's so that the chain is as follows:

Active terminator
CSPPC
IBM ID0 - no term power
Seagate ID1 - term power
CD-ROM ID2 - no term power
Active terminator

When I have that chain I still go to the kickstart 3.1 boot menu.

When I remove the CD-ROM it boots into OS4.1 fine (placed on the IBM).

I most admit I am loosing hope here. Once during my fideling around I got the CD to work. Then I put all hardware in its places and changed som ID jumpers and then it didn't work again. Do not know why? :-(

I have an old IDE DVD-drive laying around. Can I use that on the IDE channel? I know it is not that fast but since I am will not be using it for anything but installation that would be just fine.

SCSI kind a suck right now ....

Is the cdrom a 68pin cdrom or are you trying to adopt a 50pin cdrom to a 68pin UWscsi chain?

Have you went into the csppc early menu and checked the scsi setting? perhaps something is off? You might set everything to auto until you get up and running.

Maybe the cdrom drive is bad? 15-20 year old scsi drives do fail sometimes.

You could use a cd/dvd drive on the internal ide with no problems. it will be slow,but as you say, something is better than nothing. Be sure to set it as master if its the only ide device.

Mech

[JohnFante]

Is the cdrom a 68pin cdrom or are you trying to adopt a 50pin cdrom to a 68pin UWscsi chain?

It is a 50pin CD-ROM with a 68pin to 50pin converter. It is a Plextor PX.32TS. Se photo. Just to be clear. It has worked fine but has stopped working because I removed a HD, attached a terminator etc.

Have you went into the csppc early menu and checked the scsi setting? perhaps something is off? You might set everything to auto until you get up and running.

I have set everything to auto. No result

Maybe the cdrom drive is bad? 15-20 year old scsi drives do fail sometimes.

I have thought about that but since it has worked flawlessly until now combined with the fact that It worked very shortly during my "fideling" and the fact that I get the same error when I use a Plextor PX-W124TS CD-ROW dirve I would say that it is unlikely.

You could use a cd/dvd drive on the internal ide with no problems. it will be slow,but as you say, something is better than nothing. Be sure to set it as master if its the only ide device.

Great :-) I will dig one out and see what happends.

[mechy]

It is a 50pin CD-ROM with a 68pin to 50pin converter. It is a Plextor PX.32TS. Se photo. Just to be clear. It has worked fine but has stopped working because I removed a HD, attached a terminator etc.



I have set everything to auto. No result



I have thought about that but since it has worked flawlessly until now combined with the fact that It worked very shortly during my "fideling" and the fact that I get the same error when I use a Plextor PX-W124TS CD-ROW dirve I would say that it is unlikely.



Great :-) I will dig one out and see what happends.

I think i see the trouble, you should be using a 68 to 50 adapter with high byte termination. The picture you have seems to show a regular 68/50 adapter.

Mech

[Zac67]

When a narrow device is connected somwhere in the middle you can simply use an ordinary adapter.
Only if you connect that device to an end and need it to provide termination (no cable terminator) then you need a half-terminating adapter to take care of the high byte.

[JohnFante]

When a narrow device is connected somwhere in the middle you can simply use an ordinary adapter.

Only if you connect that device to an end and need it to provide termination (no cable terminator) then you need a half-terminating adapter to take care of the high byte.

I moved the CD-ROM to the middle of the chain and changed the ID's so that it is:

Active terminator
CSPPC
IBM ID0 - no term power
CD-ROM ID2 - no term power
Seagate ID5 - term power
Active terminator

Stil the same. :-(

Maybe my terminator is no good? It has no LED so I can not see if it has termination power. But when I remove it (and the CD-ROM) my system will not boot so it must be doing someting.

[JohnFante]

Just a quick thought after I browsed for help.

Do the HD's have to be set for single ended? There is a jumper on both that can force single ended. At the moment they are off.

The drives are a IBMDRHS-36D and a Seagate ST150176LW.

[zipper]

Just a quick thought after I browsed for help.

Do the HD's have to be set for single ended? There is a jumper on both that can force single ended. At the moment they are off.

Yes!!!

[psxphill]

Single Ended was abandoned beyond Ultra SCSI because of this. All later standards used Low Voltage Differential signaling.

And you can't mix SE and LVD on the same bus. Back when SCSI was popular you'd get servers with an UWSCSI raid controller for the harddrives and another SCSI2 controller for running the optical drives.
 
If you've still not got it sorted and you want to have them on the same bus then you will need to read up alot more on SCSI and do some trial an error adding and removing devices.

[JohnFante]

And you can't mix SE and LVD on the same bus. Back when SCSI was popular you'd get servers with an UWSCSI raid controller for the harddrives and another SCSI2 controller for running the optical drives.
 
If you've still not got it sorted and you want to have them on the same bus then you will need to read up alot more on SCSI and do some trial an error adding and removing devices.

My HD's kan do both SE and LVD.

I will se if forcing SE gives any result. If not then I will switch to a IDE CD-ROM and give  my SCSI-problem a rest and read up on SCSI.

I am a bit tired off moving drives and jumpers around .... :-)