----- Original Message ----- From: Jonathan Morton <[email protected]>
On 22 Jan, 2014, at 11:34 pm, Lee Kolb wrote: > 1,2,4, parity, sector size, terminator, and term. power. > I'm puzzled by the first three, because I thought the max. no of SCSI devices > was 6 "Narrow SCSI" as found in old Macs can have device IDs from 0-7, where 7 is 1+2+4, a standard 3-bit binary code. ID 7 is usually reserved for the controller, which is just a device on the bus which happens to be the Mac itself. So there can be 7 "slave" devices (0-6) plus the controller. The internal CD-ROM in a Mac is usually ID 3, so since this is a replacement for that, set jumpers 1 and 2, and leave 4 open. You'll also need to set the Parity jumper, to ensure that an odd number of ID jumpers are set in total. > and I have no idea how the other four should be set Each physical end of the SCSI bus should be terminated to prevent reflections of signals from causing interference. However, this is one of the black arts of SCSI. If in doubt, look more closely at how the old drive was jumpered, and assume that any features that are new on the replacement drive should be left unselected. If the CD-ROM is on the *last* connector of the cable and there *isn't* an external terminator at that point (you'll be able to see it easily), then set the terminator jumper. If the CD-ROM is on the *last* connector and there *is* an external terminator, set the "terminator power" jumper instead. That'll allow the external terminator to work. If the internal hard disk is on the last connector, so that the CD-ROM is *not* physically the last device, then leave both the terminator jumpers open. There should *not* be an external terminator at that connector. ------------------------------------------------------- The Performa 637 has an IDE (PATA) hard drive. Not sure how that will enter into the solution. I assume the CD-ROM is on the SCSI bus. From my experience jumping or not jumping term pwr on these old CD-ROM's does not make any difference. I do have a similar Performa in cold storage (12F is the current temp) and don't want to venture into the garage to check jumper settings. Excellent explanation of SCSI basics. --glen -- -- ----- 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 [email protected] To leave this group, send email to [email protected] 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 [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
