schum...@valencia.rsn.hp.com writes: >> Yes, we do it all the time. We run both SCSI-1 and SCSI-2 (single and >> differential). We try to keep the cables as short as possible but some >get >> up to 18" long. We have not had any serious problems internally using >> standard 50 conductor flat ribbon. I did have EMI problems from the >flat, >> unshielded cables, but solved that in other ways. > >Could you elaborate on the problems and your solutions? > <<snip>>
If you are asking about EMI pronblems, I can tell you the following: One group of problem frequencies were treated at the board level. We looked at the signals and found reflections. These were corrected with terminating resistors. Care was taken to not affect the waveshape any more than necessary. Another set of frequencies was taken care of by re-routing the cable away from what turned out to be a slot antenna in the skins. A third set of frequencies was handled by a ferrite at the source (flat ferrite on the cable at the board connector). This problem was only in one configuration of the product. In a different product we ended up solving our EMI problems by solving our performance problems, that is, we needed higher data rates with longer cables external. By going to differential SCSI, both sets of problems went away. We did not ever appear to have cross-talk or other signal integrity problems that I am aware of. I do know that the Development guys spent quite a bit of time evaluating the SCSI channel, I think more in terms of data rates vs. cable lengths rather than integrity problems. I also know they spent a lot of time looking at SCSI drives and settled for a 7,200 rpm 8 ms drive. We make imagers and needed data rates of 8 MB/sec or so. They also incorporated line buffers in the product interface. If they did anyting in firmware to correct for any problems, I do not know. Hope this helps. Scott s_doug...@ecrm.com --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
