fausett@aivax.radc.af.mil (Mark L. Fausett) (02/08/91)
I'm trying to attach a CDC Wreh VI to a NeXT machine. It formats, and reads very nicely. I'm getting scsi timeouts on writes though (write EVENTUALLY succeed, but several orders of magnitude delay over reads). I figure I've probably screwed the termination, cable impedance or both. Could this cause this symptom, if so, what is the proper cable impedance, and is the termination 220 or 330 ohms (or something else??) Thanks, Mark Fausett fausett@aivax.radc.af.mil
whit@milton.u.washington.edu (John Whitmore) (02/08/91)
In article <fausett.665954939@aivax> fausett@aivax.radc.af.mil (Mark L. Fausett) writes: > ..... what is the proper cable impedance, and is the termination >220 or 330 ohms (or something else??) The original recommended termination was 330 Ohms to ground _and_ 220 Ohms to +5V; the Thevenin equivalent 130 Ohms to +3V was also recommended. I understand that the SCSI-2 spec includes a third recommendation, 110 Ohms to 2.85V. None of these values is critical (I have heard from one manufacturer that he plugged in all his resistor packs backward; everything worked, and the product actually shipped that way for a while.) I have found that a voltmeter on each pin of the cable gives 3V or ground on almost every pin (two pins may have +5V terminator power). Suspect a broken wire or faulty termination resistor, and track it down with the VOM. John Whitmore