andrewt@watsnew.waterloo.edu (Andrew Thomas) (11/14/89)
In a recent conversation with our lab manager, I was told that it is possible that Apple's SCSI interface is not consistent with the SCSI standard. In light of the advertising in this group for Apple SCSI drives at low prices, I felt that this issue might be of interest. Does anybody know whether Apple has modified their SCSI definition sufficiently that Mac drives would not work with Amiga controllers? It certainly would not come as a shock given Apple's attitude toward industry standards and interchangeability. The advertising for the cheap drives very conspicuously says *should work* with Amiga controllers. It has not been tested. -- Andrew Thomas andrewt@watsnew.waterloo.edu Systems Design Eng. University of Waterloo "If a million people do a stupid thing, it's still a stupid thing." - Opus
jea@merlin.cvs.rochester.edu (Joanne Albano) (11/15/89)
I am using a drive packaged for a mac that is completely
compatible with my Starboard SCSI interface!
.
Joanne Albano, Center for Visual Science (716) 275-3055
Room 256 Meliora Hall, Univ. of Rochester, Rochester NY 14627
UUCP: {rutgers,allegra,decvax}!rochester!ur-cvsvax!jea
INTERNET: jea@snipe.cvs.rochester.edumark@isi.UUCP (Mark Bailey) (11/15/89)
In article <4040@ur-cc.UUCP>, jea@merlin.cvs.rochester.edu (Joanne Albano) writes: > I am using a drive packaged for a mac that is completely > compatible with my Starboard SCSI interface! > . > > Joanne Albano, Center for Visual Science (716) 275-3055 According to Microbotics, the Starboard SCSI interface was intended to work with Macintosh-compatable SCSI drives. (These are the recommended and tested drives) -- Mark Bailey (I didn't really say this.) via: ...!uunet!pyrdc!isi!mark ------Have a 8-| day!!!!!
charles@hpcvca.CV.HP.COM (Charles Brown) (11/16/89)
> In a recent conversation with our lab manager, I was told that it is > possible that Apple's SCSI interface is not consistent with the SCSI > standard. > Andrew Thomas I have a Miniscribe (sorry I don't remember the part #) SCSI drive connected to a 2090A controller. The Miniscribe was billed as Mac compatible. It works on the A2000 except that it will not autoboot (not even from a warm boot). I assume it works with a Mac. I contacted Miniscribe and Commodore about this several times. The result was that Miniscribe was eager to talk to Commodore to work out the problem. Commodore showed no interest in talking to Miniscribe. The Commodore rep said the Miniscribe drive is not meeting the SCSI spec and that Commodore was NOT going to change the 2090A to work with it. The particular spec involved the time from reset to ready. The Commodore will not autoboot if that time is greater than (as I recall) four seconds. The Miniscribe appears (from my informal measurements) to take about 5 seconds if warm booting with the head on track 2, about 8 seconds if warm booting with the head near the middle track, and about 14 seconds from power up. I boot from floppy. I am not happy about this, but am not interested in tossing out a otherwise excellent drive. I am also not interested in buying an additional hard drive JUST for booting. -- Charles Brown charles@cv.hp.com or charles%hpcvca@hplabs.hp.com or hplabs!hpcvca!charles or "Hey you!" Not representing my employer. "The guy sure looks like plant food to me." Little Shop of Horrors
morris-ng@cup.portal.com (Yuklung Morris Ng) (11/16/89)
When you see an ad for Amiga SCSI controllers, they usually mention they are compatible with Mac drive. I have tried to use a Fujitsu drive for Mac. It worked for me, though I am not using it right now. I am using HardFrame, by the way. - Morris
steveb@cbmvax.UUCP (Steve Beats) (11/17/89)
In article <1410034@hpcvca.CV.HP.COM> charles@hpcvca.CV.HP.COM (Charles Brown) writes: >[stuff deleted] > >The particular spec involved the time from reset to ready. The >Commodore will not autoboot if that time is greater than (as I recall) >four seconds. The Miniscribe appears (from my informal measurements) >to take about 5 seconds if warm booting with the head on track 2, >about 8 seconds if warm booting with the head near the middle track, >and about 14 seconds from power up. > The problem is not the time from RESET to ready, but the time from RESET to response to commands. Seagate drives have this same problem. When the drive is spinning up from cold start, it does not respond to selection at all. This looks to the driver software as if no drive is hooked up. The solution is to try for selection, if it fails wait a second and try again up to a timeout limit. However, SCSI drivers have to check 7 distinct SCSI bus addresses to see if drives are hooked up (there is a way under the new RDB scheme to shortcut this check, but that`s not important here). If the driver were to assume that all drives took at least 5 seconds to spin up, that would be 7*5 = 35 seconds of dead time on a cold boot. Since the majority of drives respond correctly, it does not make sense to compromise systems with good drives for the few with bad ones (bad meaning badly behaved). This problem has been (sort of) addressed on the A590 and A2091 by having a "Seagate" jumper on the board. If this jumper is installed, much longer timeouts are allowed when cold booting the system. Steve
bevis@EE.ECN.PURDUE.EDU (Jeff Bevis) (11/18/89)
In article <8608@cbmvax.UUCP>, steveb@cbmvax.UUCP (Steve Beats) writes: >In article <1410034@hpcvca.CV.HP.COM> charles@hpcvca.CV.HP.COM (Charles Brown) writes: >up to a timeout limit. However, SCSI drivers have to check 7 distinct ^^^^^^^^^^^^^^^^^^^^^^^^ >SCSI bus addresses to see if drives are hooked up (there is a way under ^^^^^^^^^^^^^^^^^^ >the new RDB scheme to shortcut this check, but that`s not important here). >If the driver were to assume that all drives took at least 5 seconds to >spin up, that would be 7*5 = 35 seconds of dead time on a cold boot. Since ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ That must explain it. I've got a supra 4x4 now, and I boot off a floppy. But when it's mounting, supramount stops and vegetates, doing nothing, eating almost no cputime for about 28 seconds. Then it boots quite rapidly. Oh, this is so frustrating. Does anybody out there know how I can inform supramount to ONLY check for scsi device 0? (I'd call Supra on Monday...) +--------------------------------+--------------------------------------------+ | Jeff Bevis | "But I don't like spam!" | | bevis@en.ecn.purdue.edu | Give me Amiga or nothing at all. | +--------------------------------+--------------------------------------------+
robertw@hpcvlx.cv.hp.com (Robert B. Williams) (11/19/89)
Re: are Macs REAL scsi... All you have to do is look at the cables... the Mac ones have ~25 pins, and the Real scsi cables have ~100. BTW I have a MB Stardrive (Mac compatible, the idiots) and a ST277n(?) scsi drive with a real scsi port. It was a LOT OF FUN making a cable for this but it works. Don't know about booting, this is on an A1000. Robert Williams robertw@CV.HP.COM Corvallis Information Systems
lphillips@lpami.wimsey.bc.ca (Larry Phillips) (11/20/89)
In <102810001@hpcvlx.cv.hp.com>, robertw@hpcvlx.cv.hp.com (Robert B. Williams) writes: >All you have to do is look at the cables... the Mac ones have ~25 pins, >and the Real scsi cables have ~100. > >BTW I have a MB Stardrive (Mac compatible, the idiots) and a ST277n(?) >scsi drive with a real scsi port. It was a LOT OF FUN making a cable for this >but it works. Don't know about booting, this is on an A1000. I'll bet it was fun! Trying to solder ~100 pins on a 50 pin SCSI connector could be a real hassle. -larry -- My name is OS/2, Mandius, Kludge of Kludges. Look upon my works, ye CS majors, and gag. +-----------------------------------------------------------------------+ | // Larry Phillips | | \X/ lphillips@lpami.wimsey.bc.ca -or- uunet!van-bc!lpami!lphillips | | COMPUSERVE: 76703,4322 -or- 76703.4322@compuserve.com | +-----------------------------------------------------------------------+
lphillips@lpami.wimsey.bc.ca (Larry Phillips) (11/20/89)
In <74147@tut.cis.ohio-state.edu>, erd@giza.cis.ohio-state.edu (Ethan R Dicks) writes: >So could Steve or someone else tell us the order that C= controllers use >in querying the SCSI bus? [ stuff deleted ] They are queried in ascending order of target address, from 0 through 6 (mountlist unit entries 3 through 9). >I.e. If the order is 0 - 7, and there is a 4 second timeout per device and >a Seagate takes up to 12 seconds to pay attention to the bus after a reset, >then the drive should be set to at least 3, giving the drive time to wait >for the controller to timeout on 0, 1 and 2. > >Is this a valid workaround? Should work. Worth a try, and can't hurt. -larry -- My name is OS/2, Mandius, Kludge of Kludges. Look upon my works, ye CS majors, and gag. +-----------------------------------------------------------------------+ | // Larry Phillips | | \X/ lphillips@lpami.wimsey.bc.ca -or- uunet!van-bc!lpami!lphillips | | COMPUSERVE: 76703,4322 -or- 76703.4322@compuserve.com | +-----------------------------------------------------------------------+
erd@giza.cis.ohio-state.edu (Ethan R Dicks) (11/20/89)
In article <8608@cbmvax.UUCP> steveb@cbmvax.UUCP (Steve Beats) writes: >In article <1410034@hpcvca.CV.HP.COM> charles@hpcvca.CV.HP.COM (Charles Brown) writes: >>[stuff deleted] >> [ more stuff deleted ] > However, SCSI drivers have to check 7 distinct >SCSI bus addresses to see if drives are hooked up (there is a way under >the new RDB scheme to shortcut this check, but that`s not important here). [ still more stuff deleted ] > > Steve So could Steve or someone else tell us the order that C= controllers use in querying the SCSI bus? Theoretically, you could set the naughty device toward the end of the chain so that several device numbers must time out before getting to the valid device, giving it time to pay attention... I.e. If the order is 0 - 7, and there is a 4 second timeout per device and a Seagate takes up to 12 seconds to pay attention to the bus after a reset, then the drive should be set to at least 3, giving the drive time to wait for the controller to timeout on 0, 1 and 2. Is this a valid workaround? -ethan -- Ethan R. Dicks | ###### This signifies that the poster is a member in Software Results Corp| ## good sitting of Inertia House: Bodies at rest. 940 Freeway Drive N. | ## Columbus OH 43229 | ###### "You get it, you're closer."
33014-18@sjsumcs.sjsu.edu (Eduardo Horvath) (11/20/89)
In article <8911180041.AA15338@en.ecn.purdue.edu> bevis@EE.ECN.PURDUE.EDU (Jeff Bevis) writes: [...] >Oh, this is so frustrating. Does anybody out there know how I can inform >supramount to ONLY check for scsi device 0? (I'd call Supra on Monday...) ^^^^^^^^^^^^^^^^^^^^^^^^ Please post the results. I *HATE* the wait! >+--------------------------------+--------------------------------------------+ >| Jeff Bevis | "But I don't like spam!" | >| bevis@en.ecn.purdue.edu | Give me Amiga or nothing at all. | >+--------------------------------+--------------------------------------------+ =============================================================================== //x = /// \ Try: 33014-18@sjsumcs.SJSU.EDU = Early to bet /// \ = And early to raise /// \ Eduardo Horvath = Makes a man poor \\\ ///=======\ = In a gamling craze! \\\/// \ = -me \xxx \miga. The computer for the corruptive mind. ===============================================================================
dak%ritcv@cs.rit.edu (340 Ok) (11/21/89)
hello, Look in Amazing computing from quite a few months ago. Then show the pin-outs for the 25pin and 50 pin SCSI connectors. It seems that half of the 50 pin cable is for grounds. That's how Apple got it down to 25 pins. They use the sheild as a return ground for the signals. I think that some of the other pins might be ground to, (I haven't looked at the pin-outs in some time). To the guy with the stardrive, how well does it work with the seagate drive? (transfer rate, utilities?) I was considering that for my starboard or getting a Comspec auto-booting SCSI controller. (I have a LUCAS and know that the Comspec will work with it.) David A. Kavanagh /-------------------------------------------------------------------------\ / David A. Kavanagh | Rochester Institute of Technology Grad CS \ < 65 Tahoe Drive |"Great spirits have always encountered violent > \ Rochester, NY 14616-1007| opposition from mediochre minds" - A. Einstein / \-------------------------------------------------------------------------/
stephen@hpdml93.HP.COM (Stephen Holmstead) (11/23/89)
David A. Kavanagh (dak%ritcv@cs.rit.edu) writes: > Look in Amazing computing from quite a few months ago. Then show the >pin-outs for the 25pin and 50 pin SCSI connectors. It seems that half >of the 50 pin cable is for grounds. That's how Apple got it down to 25 >pins. They use the sheild as a return ground for the signals. I think >that some of the other pins might be ground to, (I haven't looked at >the pin-outs in some time). Just a warning to people who want to get rid of 50 pin SCSI connectors (eg. Apple Computer): Half of the pins on a 50 pin connector are grounds ONLY on a single-ended SCSI device. On differential SCSI devices, all 50 pins are used. When Apple went to a 25 pin SCSI port, they made a statement that do not want to consider anything but a single-ended SCSI device. In the *REAL* world, people use 50 pins for both single-ended and differential drives, thus creating a 'standard' (heaven forbit if Apple ever used a 'standard' cable!). :-) Just thought everybody in net-land would like to know before we started getting the "why do we have 50 pin SCSI connectors anyway?" articles. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Stephen Holmstead ...!hplabs!hpdmlge!stephen // Hewlett Packard Disk Memory Division \X/ Amiga Forever! "I remind you that humans are only a tiny minority in this galaxy." -- Spock, "The Apple," stardate 3715.6.
dawill@hubcap.clemson.edu (david williams) (11/28/89)
In article <15450001@hpdml93.HP.COM>, stephen@hpdml93.HP.COM (Stephen Holmstead) writes: > Just a warning to people who want to get rid of 50 pin SCSI connectors > (eg. Apple Computer): Half of the pins on a 50 pin connector are > grounds ONLY on a single-ended SCSI device. On differential SCSI > devices, all 50 pins are used. When Apple went to a 25 pin SCSI port, > they made a statement that do not want to consider anything but a > single-ended SCSI device. In the *REAL* world, people use 50 pins for > both single-ended and differential drives, thus creating a 'standard' > (heaven forbit if Apple ever used a 'standard' cable!). :-) > Hummm. I am in the process of hacking together a 50pin-to-25pin connector for a StarDrive I recently got. The target drive (my roomate's) is a miniscribe 8425S. Is this drive differential? If not, how often is differential drive used in the REAL world? I have a feeling that this would only be used on really high-end drives, much as professional audio uses balanced connectors, and consumer stuff only uses single-ended. Dave Williams dawill@hubcap.clemson.edu DAVE...DAVe...DAve...Dave...dave "You think I'd really tell you what I'm up to?"
charles@hpcvca.CV.HP.COM (Charles Brown) (11/29/89)
>>The particular spec involved the time from reset to ready. The >>Commodore will not autoboot if that time is greater than (as I recall) >>four seconds. The Miniscribe appears (from my informal measurements) >>to take about 5 seconds if warm booting with the head on track 2, >>about 8 seconds if warm booting with the head near the middle track, >>and about 14 seconds from power up. > The problem is not the time from RESET to ready, but the time from RESET > to response to commands. Seagate drives have this same problem. When the > drive is spinning up from cold start, it does not respond to selection at > all. This looks to the driver software as if no drive is hooked up. The > solution is to try for selection, if it fails wait a second and try again > up to a timeout limit. That is fine, except that the COMPETITOR's computers will successfully boot from these same disk drives. The customer does not say "what a pity my computer works with this drive when the drive is out of spec". The customer (me) says "I am not happy that the Amiga fails to boot with this drive. The other computer can, why not the Amiga?" > However, SCSI drivers have to check 7 distinct > SCSI bus addresses to see if drives are hooked up (there is a way under > the new RDB scheme to shortcut this check, but that`s not important here). > If the driver were to assume that all drives took at least 5 seconds to > spin up, that would be 7*5 = 35 seconds of dead time on a cold boot. Not true. The Amiga only attempts to autoboot from the first SCSI. So if the delay is extended to 10 seconds, the max wait would be 10 seconds. Notice that a customer would rarely see this delay. The algorithm looks something like: if there is a floppy boot from it no delay else if there is a ST506 boot from it short delay? else loop once a second did the SCSI respond? yes: boot from it delay of 1 to 10 seconds depending on how fast the drive responds no: prompt for a floppy <-- max delay slightly over 10 sec > Since > the majority of drives respond correctly, it does not make sense to > compromise systems with good drives for the few with bad ones (bad meaning > badly behaved). Compromised! The only delay this affects is the time to display the hand, and that delay only occurs if the following is true there is not a floppy in the drive AND there is a 2090A card AND there is not a bootable ST506 drive AND there is not a bootable SCSI drive Realistically, how often is that going to happen? That low probability is what you are balancing against the cost of having a number of drives which will not boot with the current firmware. It looks to me like about 30% of hard drives will not boot because of this spec. The 2090 users's guide (with the addendum) lists 8 that do and 4 that don't autoboot. If I include my data point (Miniscribe 3180S) that works out to 5/13=38% of known SCSI drives which will not autoboot. > This problem has been (sort of) addressed on the A590 and > A2091 by having a "Seagate" jumper on the board. If this jumper is > installed, much longer timeouts are allowed when cold booting the system. > steveb@cbmvax.UUCP (Steve Beats) I bought the A2090A because it was supposed to autoboot. Now it appears I need to buy the A2091 to autoboot. I hope you understand my frustration. -- Charles Brown charles@cv.hp.com or charles%hpcvca@hplabs.hp.com or hplabs!hpcvca!charles or "Hey you!" Not representing my employer.
stephen@hpdml93.HP.COM (Stephen Holmstead) (11/30/89)
dawill@hubcap.clemson.edu (david williams) writes: > Hummm. I am in the process of hacking together a 50pin-to-25pin connector >for a StarDrive I recently got. The target drive (my roomate's) is a miniscribe >8425S. Is this drive differential? If not, how often is differential drive >used in the REAL world? I have a feeling that this would only be used on >really high-end drives, much as professional audio uses balanced connectors, and >consumer stuff only uses single-ended. Yup. Differential drives are mostly used on high-end systems. The SCSI bus uses +12V and -12V signal levels as opposed to +5v and GND used on Single-ended drives. Obviously, the differential drives are not as sensitive to say a 2V signal drop as would a single-ended drive. NOTE TO EVERYONE WHO IS WORRIED IF THEY HAVE A DIFFERENTIAL DRIVE ON THEIR AMIGA: All of the SCSI controllers that I know of for the Amiga use single-ended SCSI. You would *REALLY* know if you put a differential drive on a single-ended controller!! :-) I would *LOVE* to see standardization of cables (eg, SCSI means 50 pin cable, serial interface means DB-25 cable, etc.). Speaking of standard cables, what possessed Commodore to use a DB-23?!?!?!? :-) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Stephen Holmstead ...!hplabs!hpdmlge!stephen // Hewlett Packard Disk Memory Division \X/ Amiga Forever! "I remind you that humans are only a tiny minority in this galaxy." -- Spock, "The Apple," stardate 3715.6.
farren@well.UUCP (Mike Farren) (11/30/89)
In article <ANDREWT.89Nov13165620@watsnew.waterloo.edu> andrewt@watsnew.waterloo.edu (Andrew Thomas) writes: > >In a recent conversation with our lab manager, I was told that it is >possible that Apple's SCSI interface is not consistent with the SCSI >standard. Well, depends. Apple SCSI is different from the standard, in that Apple chose to use a 25-pin connector instead of the defined 50-pin connector, thereby losing all of the extra grounds the standard provides, and also losing the ability to use long SCSI cables reliably. (Notice that Apple recommends a max cable length of only 1 meter?) Many Amiga controllers, however, offer an Apple-compatible 25-pin connector, and Mac drives should work on these with no problems whatsoever - the rest of the interface is pretty much standard. -- Mike Farren farren@well.sf.ca.usa
lphillips@lpami.wimsey.bc.ca (Larry Phillips) (11/30/89)
In <15450003@hpdml93.HP.COM>, stephen@hpdml93.HP.COM (Stephen Holmstead) writes: >I would *LOVE* to see standardization of cables (eg, SCSI means 50 pin >cable, serial interface means DB-25 cable, etc.). Speaking of standard >cables, what possessed Commodore to use a DB-23?!?!?!? :-) This is the second comment I have seen recently wondering why CBM used a DB-23. Thankfully, yours was not in the nature of a flame. There is a very good reason. Take a look at the back of an IBM or clone sometime, and tell me how many ways you can plug the wrong thing into the wrong place. Now do the same with the Amiga. Many folks have fried things on the clones, because they plugged something in wrong. Additionally, the two devices that do have the 23 pin connectors are not 'standard' in the industry. The floppy in particular has an extra bit of interface that means you cab't just plug in a stock clone floppy, and that you can't just use an Amiga floppy on anything but an AMiga. It was only a slight problem for a few months, until DB-23s became more available. While I'm at it, I may as well voice my pet peeve about connectors. IBM did the RS-232 WRONG. I know it isn't in the spec, but up until these clowns got hold of it, most manufacturers used FEMALE connectors on their equipment (not as easy to short out). Now we have CBM, who did it right on the A1000, then decided to kowtow to the IBMishness and use a male RS-232. Grr. -larry -- " All I ask of my body is that it carry around my head." - Thomas Alva Edison - +-----------------------------------------------------------------------+ | // Larry Phillips | | \X/ lphillips@lpami.wimsey.bc.ca -or- uunet!van-bc!lpami!lphillips | | COMPUSERVE: 76703,4322 -or- 76703.4322@compuserve.com | +-----------------------------------------------------------------------+
charles@hpcvca.CV.HP.COM (Charles Brown) (11/30/89)
> Hummm. I am in the process of hacking together a 50pin-to-25pin > connector for a StarDrive I recently got. The target drive (my > roomate's) is a miniscribe 8425S. Is this drive differential? No. SCSI is not differential. It merely (most of the time) interdigitates signals and grounds in the 50 wire ribbon cable. Sort of a poor man's differential drive. > If not, how often is differential drive used in the REAL world? I > have a feeling that this would only be used on really high-end > drives, much as professional audio uses balanced connectors, and > consumer stuff only uses single-ended. > Dave Williams > dawill@hubcap.clemson.edu Rarely. Don't worry about it. -- Charles Brown charles@cv.hp.com or charles%hpcvca@hplabs.hp.com or hplabs!hpcvca!charles or "Hey you!" Not representing my employer.
ridder@elvira.enet.dec.com (Hans Ridder) (12/01/89)
In article <1410036@hpcvca.CV.HP.COM> charles@hpcvca.CV.HP.COM (Charles Brown) writes: >> Hummm. I am in the process of hacking together a 50pin-to-25pin >> connector for a StarDrive I recently got. The target drive (my >> roomate's) is a miniscribe 8425S. Is this drive differential? > >No. SCSI is not differential. It merely (most of the time) >interdigitates signals and grounds in the 50 wire ribbon cable. >Sort of a poor man's differential drive. No, SCSI *can be* differential. The SCSI specification clearly defines two electrical interfaces. One is differential, the other "single-ended". The single-ended version is probably more popular because is it cheaper to implement. Please know what you're talking about before posting assertions like this. >> Dave Williams >> dawill@hubcap.clemson.edu >-- > Charles Brown charles@cv.hp.com or charles%hpcvca@hplabs.hp.com > or hplabs!hpcvca!charles or "Hey you!" > Not representing my employer. -hans ======================================================================== Hans-Gabriel Ridder Digital Equipment Corporation ridder@elvira.enet.dec.com Customer Support Center ...decwrl!elvira.enet!ridder Colorado Springs, CO
charles@hpcvca.CV.HP.COM (Charles Brown) (12/03/89)
>>No. SCSI is not differential. It merely (most of the time) >>interdigitates signals and grounds in the 50 wire ribbon cable. >>Sort of a poor man's differential drive. > No, SCSI *can be* differential. The SCSI specification clearly > defines two electrical interfaces. One is differential, the other > "single-ended". The single-ended version is probably more popular > because is it cheaper to implement. Indeed I was confusing the standard with the implementation. There is an OPTION in the standard to allow differential drive. So can anyone name a product which actually uses the differential drive option? Certainly not the Amiga. > Please know what you're talking > about before posting assertions like this. > Hans-Gabriel Ridder Digital Equipment Corporation Please be less abusive in your corrections. Have you ever made a mistake? -- Charles Brown charles@cv.hp.com or charles%hpcvca@hplabs.hp.com or hplabs!hpcvca!charles or "Hey you!" Not representing my employer.
ridder@elvira.cxo3.dec.com (Hans Ridder) (12/05/89)
In article <1410038@hpcvca.CV.HP.COM> charles@hpcvca.CV.HP.COM (Charles Brown) writes: > >> Please know what you're talking about before posting assertions >> like this. >> Hans-Gabriel Ridder Digital Equipment Corporation > >Please be less abusive in your corrections. Have you ever made a >mistake? >-- > Charles Brown charles@cv.hp.com or charles%hpcvca@hplabs.hp.com Since Charles posted, I will post my reply. I'm sorry if I seemed abusive, I didn't intend it to be taken harshly. I was just trying to point out that facts should be checked before making absolute statments such as yours. I have seen phrases like mine used on the net before with no *apparent* recrimination. Your objection has been noted. And yes, I make lots of mistakes. -hans ======================================================================== Hans-Gabriel Ridder Digital Equipment Corporation ridder@elvira.enet.dec.com Customer Support Center ...decwrl!elvira.enet!ridder Colorado Springs, CO
lphillips@lpami.wimsey.bc.ca (Larry Phillips) (12/05/89)
In <593@bmers58.UUCP>, keithh@atreus.uucp (Keith Hanlan) writes: > What is meant by "differential SCSI"? > What is meant by "single-ended SCSI"? On any wire that carries an electrical signal, you always need to have another wire that serves as a reference. If you only have one wire, you can send all the signals you want down it, and the other end will not be able to tell anything about the signal. A differential line is one that has changing signals on both wires. One pushes, one pulls, as it were. As an example, wire A might go to +5 V, while wire B goes to -5V. When wire A goes to -5V, wire B would go to +5V. A single ended scheme has one wire changing states, say from 0 to +5V, while the other wire sorta says "You push, you pull, I'm gonna just sit here at 0V." > Is this something to do with chaining devices? Not really. It does mean that the circuitry has to be correct for the method on all devices on the line; you can't mix differential and single-ended methods. It also works out that differential methods are less noise prone and can generally drive a longer cable. -larry -- " All I ask of my body is that it carry around my head." - Thomas Alva Edison - +-----------------------------------------------------------------------+ | // Larry Phillips | | \X/ lphillips@lpami.wimsey.bc.ca -or- uunet!van-bc!lpami!lphillips | | COMPUSERVE: 76703,4322 -or- 76703.4322@compuserve.com | +-----------------------------------------------------------------------+
keithh@atreus.uucp (Keith Hanlan) (12/05/89)
In article <15450001@hpdml93.HP.COM>, stephen@hpdml93.HP.COM (Stephen Holmstead) writes: > Just a warning to people who want to get rid of 50 pin SCSI connectors > (eg. Apple Computer): Half of the pins on a 50 pin connector are > grounds ONLY on a single-ended SCSI device. On differential SCSI > devices, all 50 pins are used. What is meant by "differential SCSI"? What is meant by "single-ended SCSI"? Is this something to do with chaining devices? Thanks, Keith Hanlan Bell-Northern Research, Ottawa, Canada 613-765-4645 uunet!utgpu!bnr-vpa!bnr-fos!bmers58!atreus!keithh or keithh@bnr.ca Keith Hanlan Bell-Northern Research, Ottawa, Canada 613-765-4645 uunet!utgpu!bnr-vpa!bnr-fos!bmers58!atreus!keithh or keithh@bnr.ca
dawill@hubcap.clemson.edu (david williams) (12/09/89)
In article <593@bmers58.UUCP>, keithh@atreus.uucp (Keith Hanlan) writes: > In article <15450001@hpdml93.HP.COM>, stephen@hpdml93.HP.COM (Stephen Holmstead) writes: > > Just a warning to people who want to get rid of 50 pin SCSI connectors > > (eg. Apple Computer): Half of the pins on a 50 pin connector are > > grounds ONLY on a single-ended SCSI device. On differential SCSI > > devices, all 50 pins are used. > > What is meant by "differential SCSI"? > What is meant by "single-ended SCSI"? > > Is this something to do with chaining devices? > Since I seem to have started this, I'll answer your question: Differential drive is a technique of sending signals to eliminate noise. You use two wires for each signal. One wire carries the normal signal, and the other wire carries the signal after being inverted. At the recieving end, you invert the signal that was inverted at the transmiter, and add them together. Any noise on the line cancels out (since each line gets the same amount of noise placed on it during the traversal of the cable) and you end up with a clean signal. Single-ended means you use just one wire for each signal, and put up with the resulting noise. As I understand it, RS-422 is much like RS-232, yet it uses differential drive. ------------------------------------------------------ /'''''\ Dave Williams | o o | dawill@hubcap.clemson.edu | m | PeopleLink: SillyDave | \___/ | Huh? What? Could you repeat the question? \__U__/ "Ha! I finally got a reallyyyyy greattttt .sig file!"
valentin@cbmvax.UUCP (Valentin Pepelea) (12/09/89)
In article <7388@hubcap.clemson.edu> dawill@hubcap.clemson.edu (david williams) writes: > > Since I seem to have started this, I'll answer your question: Differential >drive is a technique of sending signals to eliminate noise. You use two wires >for each signal. One wire carries the normal signal, and the other wire carries >the signal after being inverted. At the recieving end, you invert the signal >that was inverted at the transmiter, and add them together. Any noise on the >line cancels out (since each line gets the same amount of noise placed on it >during the traversal of the cable) and you end up with a clean signal. Not quite. Adding the inversion of the inverted signal to the positive signal will result in the doubling of the amplitude of the signal. However, the noise is in no way eliminated. It too in fact increseas in magnitude, but does not double because it is random by nature. That means that some times you get spikes which are as high as double in usual magnitude, and sometimes you get lucky ang get a cancel out. Visualise this as adding two sinusoidal waves of different magnitude together. Do they cancel each other out? What is the magnitude of the resultant wave? Valentin -- The Goddess of democracy? "The tyrants Name: Valentin Pepelea may distroy a statue, but they cannot Phone: (215) 431-9327 kill a god." UseNet: cbmvax!valentin@uunet.uu.net - Ancient Chinese Proverb Claimer: I not Commodore spokesman be
riley@batcomputer.tn.cornell.edu (Daniel S. Riley) (12/10/89)
In article <8910@cbmvax.UUCP> valentin@cbmvax.UUCP (Valentin Pepelea) writes: >In article <7388@hubcap.clemson.edu> dawill@hubcap.clemson.edu (david williams) writes: >> Since I seem to have started this, I'll answer your question: Differential >>drive is a technique of sending signals to eliminate noise. You use two wires >>for each signal. One wire carries the normal signal, and the other wire carries >>the signal after being inverted. At the recieving end, you invert the signal >>that was inverted at the transmiter, and add them together. Any noise on the >>line cancels out (since each line gets the same amount of noise placed on it >>during the traversal of the cable) and you end up with a clean signal. >Not quite. Adding the inversion of the inverted signal to the positive signal >will result in the doubling of the amplitude of the signal. However, the noise >is in no way eliminated. Random noise is not eliminated. I suppose it increases in amplitude by sqrt(2), or some such. A big win in many environments is that external interference which affects the two lines identically (emi, ground or power supply fluctuations, etc.) does cancel completely. I believe it's also possible to reduce emi from your transmission line by using differential transmission, which makes it a good choice for emi sensitive applications as well as emi "noisy" areas. disclaimer: I'm not an EE, just a physicist at a lab where we have to deal with electronics in extremely emi "noisy" environments (including everything from the usual sorts of digital switching spikes all the way up to massive amounts of synchrotron radiation). -Dan Riley (riley@tcgould.tn.cornell.edu, cornell!batcomputer!riley) -Wilson Lab, Cornell University
dawill@hubcap.clemson.edu (david williams) (12/14/89)
In article <8910@cbmvax.UUCP>, valentin@cbmvax.UUCP (Valentin Pepelea) writes: > In article <7388@hubcap.clemson.edu> dawill@hubcap.clemson.edu (david williams) writes: > > > > Since I seem to have started this, I'll answer your question: Differential > >drive is a technique of sending signals to eliminate noise. You use two wires > >for each signal. One wire carries the normal signal, and the other wire carries > >the signal after being inverted. At the recieving end, you invert the signal > >that was inverted at the transmiter, and add them together. Any noise on the > >line cancels out (since each line gets the same amount of noise placed on it > >during the traversal of the cable) and you end up with a clean signal. > > Not quite. Adding the inversion of the inverted signal to the positive signal > will result in the doubling of the amplitude of the signal. However, the noise > is in no way eliminated. It too in fact increseas in magnitude, but does not > double because it is random by nature. That means that some times you get > spikes which are as high as double in usual magnitude, and sometimes you get > lucky ang get a cancel out. > > Visualise this as adding two sinusoidal waves of different magnitude together. > Do they cancel each other out? What is the magnitude of the resultant wave? > Um. You seem to be missing one vital point here: most differential cables have the inverted and non-inverted wire pairs twisted. According to my physics book, this means both wires get AN EQUAL AMOUNT OF NOISE ON THEM. So, when we invert the - signal, the noise is inverted and cancels. It dosen't matter how random it is, as long as the amount of noise on the + and - lines are the same, it goes away at the reciever. Don't believe me? Come down to WSBF in Clemson, and I'll talk to you over a 1200 foot piece of twisted pair cable sitting next to a large 60Hz transforer and a HAM radio transmitter. Funny, I don't hear any noise. (Each end of my cable is driven by a SHURE remote broadcasting mixer.) Most stuff in audio differential uses a signal that is 1/2 of the desired signal on each wire, resulting in a unit signal at the reciever. ------------------------------------------------------- /'''''\ Fake sig file - at a CTS terminal | o o | Dave Williams dawill@hubcap.clemson.edu | m | "Huh? What? Could you repeat the question?" | \___/ | \__U__/