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  • Route [SCSI] cable with care

    From Louis Ohland@ohland@charter.net to comp.sys.ibm.ps2.hardware on Sun Mar 16 09:48:55 2025
    From Newsgroup: comp.sys.ibm.ps2.hardware

    Did you ever wonder about the very strict flat SCSI cable routing on the
    Model 90 or Model 95?

    Book of SCSI 2nd Edition https://archive.org/download/The_Book_of_SCSI_2nd_Edition/The_Book_of_SCSI_2nd_Edition.pdf

    Page 211

    "Route cable with care.
    Avoid practices such as rolling the cable up on itself, running the
    cable alongside metal for long lengths, or routing the cable past noise generators (such as power supplies). Placing the cable near ground
    planes created by grounded metal cabinetry reduces its impedance. For
    example, the free air impedance of an unshielded 28 AWG, 0.05-inch center-ribbon cable is about 105 ohms, but direct contact with a metal
    ground plane cuts that by 61 ohms. Such an impedance discontinuity will
    cause signal reflections. The SCSI-3 working group suggests that, in
    order to minimize discontinuities due to local impedance variation, a
    flat cable should be spaced at least 1.3mm (0.05 inch) from other
    cables, any other conductor, or the cable itself when the cable is folded."
    --- Synchronet 3.20c-Linux NewsLink 1.2
  • From MEK@devol95@hotmail.com to comp.sys.ibm.ps2.hardware on Mon Mar 17 12:13:04 2025
    From Newsgroup: comp.sys.ibm.ps2.hardware

    On 16/3/25 22:48, Louis Ohland wrote:
    Did you ever wonder about the very strict flat SCSI cable routing on the Model 90 or Model 95?

    Book of SCSI 2nd Edition https://archive.org/download/The_Book_of_SCSI_2nd_Edition/ The_Book_of_SCSI_2nd_Edition.pdf

    Page 211

    "Route cable with care.
     Avoid practices such as rolling the cable up on itself, running the
    cable alongside metal for long lengths, or routing the cable past noise generators (such as power supplies). Placing the cable near ground
    planes created by grounded metal cabinetry reduces its impedance. For example, the free air impedance of an unshielded 28 AWG, 0.05-inch center-ribbon cable is about 105 ohms, but direct contact with a metal ground plane cuts that by 61 ohms. Such an impedance discontinuity will cause signal reflections. The SCSI-3 working group suggests that, in
    order to minimize discontinuities due to local impedance variation, a
    flat cable should be spaced at least 1.3mm (0.05 inch) from other
    cables, any other conductor, or the cable itself when the cable is folded."
    I have seen the twisted ones naked *me aculpa*
    but those were long very long!
    --
    Moussa

    "People alike with a similar circumstances, tend to find each
    others across space and time, given enough time in life, no
    matter distance, language, race, colour and believes" (c) MEK
    *** Do Not Copy, Duplicate or Use without my Permission ***
    --- Synchronet 3.20c-Linux NewsLink 1.2
  • From MEK@devol95@hotmail.com to comp.sys.ibm.ps2.hardware on Tue Mar 18 10:17:20 2025
    From Newsgroup: comp.sys.ibm.ps2.hardware

    On 17/3/25 12:13, MEK wrote:
    On 16/3/25 22:48, Louis Ohland wrote:
    Did you ever wonder about the very strict flat SCSI cable routing on
    the Model 90 or Model 95?

    Book of SCSI 2nd Edition
    https://archive.org/download/The_Book_of_SCSI_2nd_Edition/
    The_Book_of_SCSI_2nd_Edition.pdf

    Page 211

    "Route cable with care.
      Avoid practices such as rolling the cable up on itself, running the
    cable alongside metal for long lengths, or routing the cable past
    noise generators (such as power supplies). Placing the cable near ground
    planes created by grounded metal cabinetry reduces its impedance. For
    example, the free air impedance of an unshielded 28 AWG, 0.05-inch
    center-ribbon cable is about 105 ohms, but direct contact with a metal
    ground plane cuts that by 61 ohms. Such an impedance discontinuity
    will cause signal reflections. The SCSI-3 working group suggests that,
    in order to minimize discontinuities due to local impedance variation,
    a flat cable should be spaced at least 1.3mm (0.05 inch) from other
    cables, any other conductor, or the cable itself when the cable is
    folded."
    I have seen the twisted ones naked *me aculpa*
    but those were long very long!

    https://www.techcable.com/internal-scsi/
    --
    Moussa

    "People alike with a similar circumstances, tend to find each
    others across space and time, given enough time in life, no
    matter distance, language, race, colour and believes" (c) MEK
    *** Do Not Copy, Duplicate or Use without my Permission ***
    --- Synchronet 3.20c-Linux NewsLink 1.2