Re: MAC LC and Internal SCSI Termination
Termination needs to be applied to both physical ends of a SCSI bus, regardless of whether they are physically inside or outside the machine, or whether one of them happens to be the controller. When both internal and external cables are present, generally the outer ends of each cable represent the extreme ends of the single bus. If the bus is physically short, however, a single terminator or sometimes no terminator at all its sufficient. A Mac with an internal drive usually has a single terminator attached to, or built into, that drive. This allows external devices to be attached while only worrying about external termination. - Jonathan Morton -- -- - You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to vintage-macs@googlegroups.com To leave this group, send email to vintage-macs+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/ --- You received this message because you are subscribed to the Google Groups Vintage Macs group. To unsubscribe from this group and stop receiving emails from it, send an email to vintage-macs+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: MAC LC and Internal SCSI Termination
Can I see the picture in question ? Sent from my iPhone On May 7, 2014, at 7:40 AM, Wesley Furr wes...@megley.com wrote: Quick question...I recently saw a photo of a Mac LC motherboard (the original one) that had a small board attached to the internal SCSI port...from what I could see of it, it looks like it may be a terminator. I know some of those units were sold with dual floppy drives and no internal hard drive. If you aren't using an internal drive on an original Mac LC, does the internal port need to be terminated? I had assumed termination on the computer side of things was automatic since there are no jumpers (that I know of) or terminating resistors to take off. Thanks, Wesley -- -- - You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to vintage-macs@googlegroups.com To leave this group, send email to vintage-macs+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/ --- You received this message because you are subscribed to the Google Groups Vintage Macs group. To unsubscribe from this group and stop receiving emails from it, send an email to vintage-macs+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout. -- -- - You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to vintage-macs@googlegroups.com To leave this group, send email to vintage-macs+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/ --- You received this message because you are subscribed to the Google Groups Vintage Macs group. To unsubscribe from this group and stop receiving emails from it, send an email to vintage-macs+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
RE: MAC LC and Internal SCSI Termination
Right...but many newer (I would guess starting around that era) SCSI controllers, at least in the PC world, have automatic termination on the controller itself. The LC would seem to be the same in that you don't have to make any changes to termination on the machine when you connect an external SCSI device...it obviously is smart enough to turn off termination for the controller...so I assumed that intelligence would follow through to not requiring an internal terminator if only external devices were attached. Finding this photo of what looks like a terminator has me wondering if that is not a correct assumption. _ From: vintage-macs@googlegroups.com [mailto:vintage-macs@googlegroups.com] On Behalf Of Jonathan Morton Sent: Wednesday, May 07, 2014 7:48 AM To: vintage-macs@googlegroups.com Subject: Re: MAC LC and Internal SCSI Termination Termination needs to be applied to both physical ends of a SCSI bus, regardless of whether they are physically inside or outside the machine, or whether one of them happens to be the controller. When both internal and external cables are present, generally the outer ends of each cable represent the extreme ends of the single bus. If the bus is physically short, however, a single terminator or sometimes no terminator at all its sufficient. A Mac with an internal drive usually has a single terminator attached to, or built into, that drive. This allows external devices to be attached while only worrying about external termination. - Jonathan Morton -- -- -- - You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to vintage-macs@googlegroups.com To leave this group, send email to vintage-macs+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/ --- You received this message because you are subscribed to the Google Groups Vintage Macs group. To unsubscribe from this group and stop receiving emails from it, send an email to vintage-macs+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
RE: MAC LC and Internal SCSI Termination
Most 68k Macs have the very simple NCR5380 SCSI controller, which most assuredly does not have automatic termination. The LC certainly doesn't have anything better than that. - Jonathan Morton -- -- - You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to vintage-macs@googlegroups.com To leave this group, send email to vintage-macs+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/ --- You received this message because you are subscribed to the Google Groups Vintage Macs group. To unsubscribe from this group and stop receiving emails from it, send an email to vintage-macs+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
RE: MAC LC and Internal SCSI Termination
OK...so let's assume we have an LC with an internal drive and nothing else. The drive and the controller are terminated such that both ends of the bus have proper termination. When you plug in an external SCSI device such as a ZIP drive, what do you change to disable termination on the controller for an LC? Thanks, Wesley Most 68k Macs have the very simple NCR5380 SCSI controller, which most assuredly does not have automatic termination. The LC certainly doesn't have anything better than that. - Jonathan Morton -- -- - You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to vintage-macs@googlegroups.com To leave this group, send email to vintage-macs+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/ --- You received this message because you are subscribed to the Google Groups Vintage Macs group. To unsubscribe from this group and stop receiving emails from it, send an email to vintage-macs+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
RE: MAC LC and Internal SCSI Termination
You don't change anything. With a single internal drive fitted, the bus is physically short enough to require only one terminator, which matches the default configuration of a Mac. The fundamental reason for termination is that electric signals tend to bounce off the end of a transmission line, and they need to be damped out within the short time permitted, so that they don't cause interference to following signals. On a short cable, the signal bounces very quickly from one end to the other, so whichever end a terminator is fitted, it is sufficient to stop the reverberation quickly enough. - Jonathan Morton -- -- - You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to vintage-macs@googlegroups.com To leave this group, send email to vintage-macs+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/ --- You received this message because you are subscribed to the Google Groups Vintage Macs group. To unsubscribe from this group and stop receiving emails from it, send an email to vintage-macs+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
RE: MAC LC and Internal SCSI Termination
Interesting...I just learned something new. I've always had it drilled in, termination, termination, termination... Also used to the PC world where there is either automatic termination, or terminating resistors that can be installed or removed. So...the LC models that shipped without an internal drive probably did have a terminator on the internal port... My main reason for curiosity is that's what I'm working towards putting together...an LC with dual internal floppies and an external hard drive. Thanks, Wesley You don't change anything. With a single internal drive fitted, the bus is physically short enough to require only one terminator, which matches the default configuration of a Mac. The fundamental reason for termination is that electric signals tend to bounce off the end of a transmission line, and they need to be damped out within the short time permitted, so that they don't cause interference to following signals. On a short cable, the signal bounces very quickly from one end to the other, so whichever end a terminator is fitted, it is sufficient to stop the reverberation quickly enough. - Jonathan Morton -- -- - You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to vintage-macs@googlegroups.com To leave this group, send email to vintage-macs+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/ --- You received this message because you are subscribed to the Google Groups Vintage Macs group. To unsubscribe from this group and stop receiving emails from it, send an email to vintage-macs+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
RE: MAC LC and Internal SCSI Termination
It may be worth remembering that for most of the original lifetime of 68k Macs, PCs did not even have PCI buses. This was an earlier era of computing than you may be thinking of, in terms of automatic termination. Selectable and pluggable termination was, however, commonly in use on both platforms. - Jonathan Morton -- -- - You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to vintage-macs@googlegroups.com To leave this group, send email to vintage-macs+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/ --- You received this message because you are subscribed to the Google Groups Vintage Macs group. To unsubscribe from this group and stop receiving emails from it, send an email to vintage-macs+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
RE: MAC LC and Internal SCSI Termination
Indeed...PCI was getting going good in the mid 90's (Wikipedia says it was created in June of 1992), and the LC dates to around 90-91 I think? I was going with the assumption that both ends must be terminated, and if there's no selection for on-board termination, then it must be automatic. I didn't realize that if the bus was short enough that you could get away with only terminating one end. I recall terminating resistors on old ISA SCSI cards, but don't remember seeing any on PCI cards...guessing the automatic termination must have started somewhere in that era...but as you say, probably after the LC. Thanks, Wesley It may be worth remembering that for most of the original lifetime of 68k Macs, PCs did not even have PCI buses. This was an earlier era of computing than you may be thinking of, in terms of automatic termination. Selectable and pluggable termination was, however, commonly in use on both platforms. - Jonathan Morton -- -- - You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to vintage-macs@googlegroups.com To leave this group, send email to vintage-macs+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/ --- You received this message because you are subscribed to the Google Groups Vintage Macs group. To unsubscribe from this group and stop receiving emails from it, send an email to vintage-macs+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: MAC LC and Internal SCSI Termination
I can confirm that diskless classic Macs did not (except for the IIfx, with it's external black SCSI terminator) ship with terminators installed on unused ports. Lacking one makes absolutely no difference, as well, having used many macs, and many, many SCSI devices. The slow SCSI busses and short cable lengths (as mentioned before) make up for a lot of SCSI sins. Built-in SCSI on Macs never really did get good, honestly, especially when compared to UNIX workstations of the day. Add-in cards were always worthwhile. - Alex On Wed, May 7, 2014 at 10:57 AM, wes...@megley.com wrote: Indeed...PCI was getting going good in the mid 90's (Wikipedia says it was created in June of 1992), and the LC dates to around 90-91 I think? I was going with the assumption that both ends must be terminated, and if there's no selection for on-board termination, then it must be automatic. I didn't realize that if the bus was short enough that you could get away with only terminating one end. I recall terminating resistors on old ISA SCSI cards, but don't remember seeing any on PCI cards...guessing the automatic termination must have started somewhere in that era...but as you say, probably after the LC. Thanks, Wesley It may be worth remembering that for most of the original lifetime of 68k Macs, PCs did not even have PCI buses. This was an earlier era of computing than you may be thinking of, in terms of automatic termination. Selectable and pluggable termination was, however, commonly in use on both platforms. - Jonathan Morton -- -- - You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to vintage-macs@googlegroups.com To leave this group, send email to vintage-macs+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/ --- You received this message because you are subscribed to the Google Groups Vintage Macs group. To unsubscribe from this group and stop receiving emails from it, send an email to vintage-macs+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout. -- -- - You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to vintage-macs@googlegroups.com To leave this group, send email to vintage-macs+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/ --- You received this message because you are subscribed to the Google Groups Vintage Macs group. To unsubscribe from this group and stop receiving emails from it, send an email to vintage-macs+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
