paul@ppgbms (Paul Evan Matz) (08/20/90)
In article <1990Aug13.011541.6424@rice.edu> devil%TECHUNIX.BITNET@cunyvm.cuny.edu (Gil Tene) writes: >X-Sun-Spots-Digest: Volume 9, Issue 302, message 9 > >- Which Suns don't provide termination power on the SCSI bus ? > (Does the Sparcstation 1,1+,SLC,IPC ?) > The SparcStation 1 and 1+, Sun3/50 and 3/60, all do not supply term power. And, I think I recall that some 3/60s even have their TERMPWR pin (pin 26) wired to ground. This can cause serious smoke if you connect a device that sources term power; The 386i seems to be the only Sun (non-VME) that sources term power, as this was required to power the external terminator plug that was supplied with that machine. Don't know about the SLC or IPC, or any of the VME-based machines; Anyone out there know??? >- If the Sun DOES provide termination power, can setting the terminators > on the drive to use the drive's power HURT anything (two power sources) ? > A device that has termination installed on it locally usually does not power it via the TERMPWR lead, but instead via its own local +5V supply. So, another device suppling TERMPWR will not cause a problem. The problem occurs when two devices are strapped to source TERMPWR; The current practice lately is for devices that supply TERMPWR to do it through a diode, so that the two sources of +5V don't "fight" with each other, as would normally happen if two power supplies were tied together in parallel. There is a reference to this issue in Sun's SCSA (Sun Common SCSI Architecture) documents. Their basic position is that any device that supplies TERMPWR must do it through a diode. This may also be a SCSI II requirement. Most devices are strap selectable, so one should be able to pick just one device to do this function, and it is only really necessary when one uses external terminators. It sure would have been nice if the initiator (CPU) had been the source, though. But, doing this may have power supply capacity & EMI implications that are better left alone. The issue of using device or external termination has gotten more complicated by seemingly increased sensitivity of the SparcStation's SCSI bus. Recently, we connected a 386i expansion box containing a 327M WREN, 150M Archive Viper, and WangDAT to a SparcStation 1+. After a few days, the machine started to get console error messages of the type: esp0: 3.0 data transfer failure etc.... The apparent reason for the problem turned out to be very interesting. Because the Sparc doesn't supply TERMPWR, it wasn't immediately clear how to use the external terminator, so instead, the last device inside the external box was terminated. This seemed OK since that is historically how Sun3 shoeboxes where terminated. I've always wondered about that segment of ribbon, between the last device and the SCSI out connector on the shoebox, though. 1-2 Ft. of ribbon past the termination does violate the intent of the SCSI spec. Well, anyway, I guess the SparcStation is more sensitive than a S3, (especially considering that creative SS1 SCSI bus implementation) because once the termination was moved from the last device to the external terminator on the SCSI out port, the error messages did stop. (In this case, it was necessary for one of the devices to source TERMPWR; Both the Viper and WangDAT are strap selectable. The WREN may be, but I don't have the manual, so I don't know). So, folks, consider yourself warned! Those of you planning to use old shoeboxes for disk storage on SS1s should consider buying a cache of external terminators. By the way, has anyone out there got a tip on suppliers of external terminators (:-) ? Cheers! ___________________________________________________________________ |Regards, PPG Biomedical Systems | |Paul Matz One Campus Drive | |914-741-4685 Pleasantville, NY. 10570 | |{..}!uunet!philabs!ppgbms!paul ppgbms!paul@philabs.philips.com | |___________________________________________________________________|
chris@com50.c2s.mn.org (Chris Johnson) (08/23/90)
In article <36040@ppgbms.UUCP> paul@ppgbms.UUCP (Paul Evan Matz) writes: >In article <1990Aug13.011541.6424@rice.edu> devil%TECHUNIX.BITNET@cunyvm.cuny.edu (Gil Tene) writes: >>X-Sun-Spots-Digest: Volume 9, Issue 302, message 9 >> >>- Which Suns don't provide termination power on the SCSI bus ? >> (Does the Sparcstation 1,1+,SLC,IPC ?) >> > >The SparcStation 1 and 1+, Sun3/50 and 3/60, all do not supply >term power. And, I think I recall that some 3/60s even have >their TERMPWR pin (pin 26) wired to ground. This can cause >serious smoke if you connect a device that sources term power; >The 386i seems to be the only Sun (non-VME) that sources term power, >as this was required to power the external terminator plug that >was supplied with that machine. Don't know about the SLC or >IPC, or any of the VME-based machines; Anyone out there know??? > >>- If the Sun DOES provide termination power, can setting the terminators >> on the drive to use the drive's power HURT anything (two power sources) ? >> > >A device that has termination installed on it locally usually >does not power it via the TERMPWR lead, but instead via its own >local +5V supply. So, another device suppling TERMPWR will not >cause a problem. The problem occurs when two devices are strapped >to source TERMPWR; The current practice lately is for devices that >supply TERMPWR to do it through a diode, so that the two sources of >+5V don't "fight" with each other, as would normally happen if two >power supplies were tied together in parallel. There is a reference >to this issue in Sun's SCSA (Sun Common SCSI Architecture) documents. >Their basic position is that any device that supplies TERMPWR must >do it through a diode. This may also be a SCSI II requirement. > >Because the Sparc doesn't supply TERMPWR, it wasn't immediately >clear how to use the external terminator, so instead, the last device >inside the external box was terminated. This seemed OK since that >is historically how Sun3 shoeboxes where terminated. I've always >wondered about that segment of ribbon, between the last device and >the SCSI out connector on the shoebox, though. 1-2 Ft. of ribbon >past the termination does violate the intent of the SCSI spec. > >Well, anyway, I guess the SparcStation is more sensitive than a S3, >(especially considering that creative SS1 SCSI bus implementation) >because once the termination was moved from the last device to >the external terminator on the SCSI out port, the error messages >did stop. (In this case, it was necessary for one of the >devices to source TERMPWR; Both the Viper and WangDAT are strap >selectable. The WREN may be, but I don't have the manual, so I >don't know). > >So, folks, consider yourself warned! Those of you planning to >use old shoeboxes for disk storage on SS1s should consider buying >a cache of external terminators. Uh, well now this is completely contrary to my experience with the Sparcstation 1/1+. They both have 125V/2A FUSES on the the TERMPWR lead, and provide nominal +5V. Either that, or my multimeter was lying. Not that this changes anything else about what Paul Matz says, however. Incidentally, Wrens have a jumper selectable terminator power source, either from TERMPWR or from internal power. They don't source (provide) TERMPWR, however. -- ...Chris Johnson chris@c2s.mn.org ..uunet!bungia!com50!chris Com Squared Systems, Inc. St. Paul, MN USA +1 612 452 9522
paul@ppgbms (Paul Evan Matz) (08/24/90)
In article <1990Aug22.170552.17671@com50.c2s.mn.org> chris@com50.c2s.mn.org (Chris Johnson) writes: > >Uh, well now this is completely contrary to my experience with the >Sparcstation 1/1+. They both have 125V/2A FUSES on the the TERMPWR >lead, and provide nominal +5V. Either that, or my multimeter was lying. Sorry for broadcasting wrong information. Chris is right about the SS1 & 1+. Just went into the lab to checked it out, and it seems his multimeter is right on. (Open mouth, insert foot...) I feel quite silly about this. The reason I thought this about the SS was due to checking a VERY old SS1 that we borrowed from our sales office for evaluation 6 months ago. I could have botched it when checking TERMPWR, but I was convinced there was no +5V present. Anyone out there have a really old original SS1 who might have noticed this? Actually I'm quite happy about the outcome of this, since we do use an external terminator; Now, at least, we don't have to decide which device is the one which should be jumpered to source TERMPWR. Again, let me apologize for the slanderous comments. ___________________________________________________________________ |Regards, PPG Biomedical Systems | |Paul Matz One Campus Drive | |914-741-4685 Pleasantville, NY. 10570 | |{..}!uunet!philabs!ppgbms!paul ppgbms!paul@philabs.philips.com | |___________________________________________________________________|