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Original question:

SN74LVC3G34: Looking for a buffer for the SPI interface

SN74LVC3G34: Seek SGPIO buffer

Andy Liu3
Intellectual 2500 points
Part Number: SN74LVC3G34
Other Parts Discussed in Thread: SN74LVC07A, SN74LVC32A, SN74AHC126, SN74ALVC126

Hi team.

My customer want to find a buffer to boost SGPIO signal.

The picture above is the standard SGPIO signal. My customer uses it for communication between the CPU and the backplane. One CPU has 2 SGPIO controllers. They share the load and dataout lines and use different clocks, no use SDatain, so there are still 4 lines in total. Please help and recommend appropriate buffer material which can buffer SGPIO signal, thanks.

Best regards,

Andy Liu

  • 0
    TI__Intellectual 2500 points

    Hi team,

    I  just check the SGPIO protocol,  the clock frequency is 100k max;

    And SGPIO signal trans to backplane board and analyzed by CPLD and then lights up the hard disk LED indicator;

    And I want to find a 3.3V Vcc, OD output, 4-ch with one OE pin, please help me check , thanks.

    Best regards,

    Andy Liu

  • 0 in reply to Andy Liu3
    Guru 244390 points

    There are no open-drain buffers with an /OE input.

    You can put OR gates (SN74LVC32A) in front of open-drain buffers (SN74LVC07A) to make the outputs Hi-Z when /OE is high.

  • 0 in reply to Clemens Ladisch
    TI__Intellectual 2500 points

    Hi Ladisch,

    Why do we need to use OR gate? I am confused, can you explain, thank you; 

    Customers just want to control these 4 channels at the same time, can we use one OE letter to connect to our 4 OE pins at the same time to achieve this function?

    And I find sn74alvc126 and sn74ahc126 are all 4-ch buffer with OD output, can they use at this circuit? 

    In fact, the output of the buffer is connected to the CPLD, and then the output of the CPLD drives the LED light, and the output of the buffer does not need to directly drive the LED.

    In fact, I didn't find the appropriate SGPIO protocol information, I'm not sure if our device can support SGPIO, please help to confirm, thank you

    Best regards,

    Andy Liu

  • 0 in reply to Andy Liu3
    Guru 244390 points

    The 74xx126 buffers do not have open-drain outputs.

    Please specify what the output should be for all four combinations of data and OE.

  • 0 in reply to Clemens Ladisch
    TI__Intellectual 2500 points

    Hi Ladisch,

    Thanks for your comments, and I have know why you recommend OR gates (SN74LVC32A) in front of open-drain buffers (SN74LVC07A);

    So our buffer SN74LVC07A can support  SFF-8485 Specification for Serial GPIO (SGPIO) Bus?

    And I will communicate with customer for deep information about the logical relationship between the four outputs and OE, and tell you tomorrow, thanks.

    Best regards,

    Andy Liu

  • 0 in reply to Andy Liu3
    Guru 244390 points

    Wikipedia says that SGPIO is a plain open-collector bus, so the 74xx07 will work fine.