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SN75LBC968: Differential signals on SN75LBC968?

Mikael Carlsen
Intellectual 270 points
Part Number: SN75LBC968
Other Parts Discussed in Thread: SN75ALS170A

Hi,


In the datasheet for SN75LBC968 on page 2 it is written:

The SN75LBC968 must be used with a SCSI
controller with support for Differential SCSI.

I cannot see that there is any differential signals at all in the datasheet (the "A" side signals). Does anyone has a clue?


I need to support up to FAST-20 speed. Suggest me any bus transceiver if this cannot be used. It should be single ended signals with Active negotation drivers.





Br Mikael

  • 0
    TI__Guru 64326 points

    Mikael,

    I would look into SN75ALS170A, it seems to be a fit for your application. 

     

  • 0 in reply to Malik Barton57
    Intellectual 270 points

    Hi Malik,

    Thanks for your answer. What I meant was that I need parallel SCSI interface with single ended signals so unfortunately SN75ALS170A doesnt fit the application.

    Br Mikael

  • 0 in reply to Mikael Carlsen
    TI__Genius 10250 points
    Hi Mikael,

    SN75LBC968 is single-ended transceiver. I'm not sure where the comment in the datasheet about differential SCSI came from. Sorry about the confusion. SN75LBC968 supports active negation and supports FAST-SCSI (not Fast-20). We don't have single-ended SCSI transceiver that supports Fast-20.

    Regards,
    Yaser
  • 0 in reply to Yaser Ibrahim
    Intellectual 270 points

    Hi Yaser,

    Thanks for the support.

    The datasheet states on p3:

    "The SN75LBC968 meets or exceeds the requirements of ANSI X3.131−1994 (SCSI-2) and the
    proposed SPI (SCSI-3) standards, and is characterized for operation from 0 ° C to 70 ° C."

    Doesn't the SCSI-3 has support for fast-20? According to Wikipedia https://en.wikipedia.org/wiki/Parallel_SCSI#SCSI-3

    SCSI-3
    Before Adaptec and later SCSITA codified the terminology, the first parallel SCSI devices that exceeded the SCSI-2 capabilities were simply designated SCSI-3.
    These devices, also known as Ultra SCSI or Fast-20 SCSI, were introduced in 1996. The bus speed doubled again to 20 MB/s for narrow (8 bit)
    systems and 40 MB/s for wide (16-bit). The maximum cable length stayed at 3 meters but single-ended Ultra SCSI developed an undeserved reputation for
    extreme sensitivity to cable length and condition (faulty cables, connectors or terminators were often to blame for instability problems).
    Unlike previous SCSI standards, SCSI-3 (Fast-20 speed) requires active termination.

    Br Mikael

  • 0 in reply to Mikael Carlsen
    TI__Genius 10250 points
    Hi Mikael,

    Sorry for the late reply. I don't know the history behind that, but it seems the terminology wasn't really settled at that time (hence the use of the word "proposed"). The SN75LBC968 datasheet explicitly says it is "Designed to operate at 10 Million Data Transfers Per Second (Fast-SCSI)".

    Regards,
    Yaser
  • 0 in reply to Yaser Ibrahim
    Intellectual 270 points

    Hi Yaser,

    Thanks for the answer.

    Br Mikael