jason@cs.utexas.edu (Jason Martin Levitt) (09/01/90)
I want to daisy chain some peripherals from a Sun 3/60.
I have a DB50 <--> Centronics SCSI cable that is supposed to
work with the 3/60.
1. I took an old tape drive from a Sun shoebox that had
and Adaptec ST506-SCSI board in it. The tape drive has
an MT02 board. I don't know anything about that board.
Is it terminated? It looks like it has two resister packs
missing, but I'm not sure. Also, it has some dip switches.
What should they be set to?
2. I bought a new Wren IV 94171-307 drive and I want to
daisy chain it with the tape drive. I removed all the
jumpers and terminator resistors except the terminator power
jumper which is set to take power from the Wren IV.
I want to externally terminate the Wren IV.
3. I want to run Centronics scsi cables from each peripheral.
Can I use the external SCSI terminator blocks that I use
with my Mac II to terminate the Sun SCSI chain?
4. One symptom I am getting is that a peripheral will not power
up when the SCSI cable from the Sun [or mac] is attached but
powers up immediately if I remove the cable. The motor start
option is disabled.
---Jason jason@cs.utexas.edugary@dgcad.sv.dg.com (Gary Bridgewater) (09/02/90)
In article <290@gort.cs.utexas.edu> jason@cs.utexas.edu (Jason Martin Levitt) writes: > > I want to daisy chain some peripherals from a Sun 3/60. >I have a DB50 <--> Centronics SCSI cable that is supposed to >work with the 3/60. > 4. One symptom I am getting is that a peripheral will not power > up when the SCSI cable from the Sun [or mac] is attached but > powers up immediately if I remove the cable. The motor start > option is disabled. This is the symptom of a cable mis-match. It was at this point that I sat down and read the Sun 3/60 pinouts and the WREN pinouts and the pinouts of the peripheral box I was using and discovered that the Sun 3/60 was, well, different. Something like SCSI A versuss SCSI-B. Why do we need more that one SCSI you ask - and I reply RS232. "Standard" means something else than what us poor users think, I guess. Never could get exteral termination to work. Tried hard. Never could get oldish 3/60 boxes to work with newish peripherals on the same wire but didn't try too hard. With a WREN VI the 70MB shoebox just wasn't that interesting anymore. -- Gary Bridgewater, Data General Corporation, Sunnyvale California gary@sv.dg.com or {amdahl,aeras,amdcad}!dgcad!gary C++ - it's the right thing to do.
steven@flood.uucp (Steven Beard) (09/06/90)
In article <290@gort.cs.utexas.edu> jason@cs.utexas.edu (Jason Martin Levitt) writes: > > I want to daisy chain some peripherals from a Sun 3/60. >I have a DB50 <--> Centronics SCSI cable that is supposed to >work with the 3/60. > > 1. I took an old tape drive from a Sun shoebox that had > and Adaptec ST506-SCSI board in it. The tape drive has > an MT02 board. I don't know anything about that board. > Is it terminated? It looks like it has two resister packs > missing, but I'm not sure. Also, it has some dip switches. > What should they be set to? The MT02 board can be terminated by inserting two resistor networks in the sockets near the SCSI connector. If you plan to use external termination these are not needed. I can dig out the part numbers if anyone really needs them. Let me know. The switches set the tape format, the SCSI address, and SCSI parity. For the Sun 3/60 they are set as follows: 1 off 2 off 3 on 4 off 5 on 6 off 7 off 8 off For more information see the MT02 manual which can be obtained from EMULEX. > > 2. I bought a new Wren IV 94171-307 drive and I want to > daisy chain it with the tape drive. I removed all the > jumpers and terminator resistors except the terminator power > jumper which is set to take power from the Wren IV. > I want to externally terminate the Wren IV. > > 3. I want to run Centronics scsi cables from each peripheral. > Can I use the external SCSI terminator blocks that I use > with my Mac II to terminate the Sun SCSI chain? The MacII external terminators will work with the Sun if terminator power is available on the SCSI cable. Unfortunately the 3/60 does not supply terminator power and to make matters worse the pin is grounded in the 3/60. You will need to modify your DB-50 to Centro 50 cable to disconnect the terminator power line to the 3/60 and then provide power to the line. Some Wren models can be jumpered to provide terminator power to the bus. It is also possible to provide terminator power from the MT02 by adding a diode (see the EMULEX manual). If neither of these options is workable, you can connect it thru a diode to the +5 supply in the disk case. Use a diode with a low voltage drop. In all cases I suggest that you add a fuse in the terminator power line to prevent accidental damage to the drive or power supply in case of problems. Values of 1 to 1 1/2 Amps are typical. We run all of our 3/60s and SPARCs in this manner and have had no problems. A word of caution is necessary regarding the type of cento 50 male-male cables used in this setup. There are currently a large number of companies importing these cables from offshore. Most of these cables are cheaply made and do not meet the SCSI specifications. These cheap cables do not use twisted pairs and are poorly sheilded. Cables which do not use twisted pair have a lot of crosstalk between the wires and do not work consistently. They often appear to work but connected devices will fail at random and the Sun may also hang randomly. Often moving the cable to flex the wires will change the behavior. The following minimum specifications are recommended for SCSI cables: 19 twisted pairs (38 wires, 19 signal, 19 ground) Both foil and braid shield Shielded connectors with cable braid connected 100% around connector The bad cables have only a foil shield and 25 wires (19 signal and 6 ground). It is often hard to find a good cable. I have had companies tell me that they meet the specification and after cutting a cable apart have found that they lied or didn't really know in the first place. Price does not seem to be much of an indicator. I have purchased $50 cables that are made wrong and $15 cables that are correct. With a little effort I can generate a list of a few companies that can supply correct cables. If anyone is interested let me know. Many companies sell both kinds or don't know what they sell so beware. As a general rule, if a companies salesman doen't understand the issue then he is selling the low quality cable. For the skeptics in the crowd I am willing to admit that the lower quality cables can work, or at least work most of the time. But I have completely trashed the file systems on two disks as a direct result of using them. Synchronous SCSI disks like the Wren-Runner almost never work reliably with the low quality cables. > > 4. One symptom I am getting is that a peripheral will not power > up when the SCSI cable from the Sun [or mac] is attached but > powers up immediately if I remove the cable. The motor start > option is disabled. This is caused by improper termination of the SCSI bus. When using the 3/60 it happens even with a terminator because the terminator power line is grounded in the 3/60. > > ---Jason jason@cs.utexas.edu Steven The Flood Group uunet!flood!steven