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SN74HC244 and SPI signals

Stefano Infante
Expert 2310 points
Other Parts Discussed in Thread: SN74HC244

Hi all!

I have a strange problem: I have to buffer an SPI port (with a sensor on it), and would like to use SN74HC244 for the job, but as I attach all cables I get no reply.

When I remove the buffers, all seems to work correctly. What could it be?

Data: SPI at 3 MHz; four SPI ports attached together (each with its buffer IC).

Can you please help?

You can find my schematics attached.

Thanks in advance.

Regards,

Stefano

  • 0
    TI__Guru* 96802 points

    Stefano,

    What voltage is this system operating at?  Is the data rate 3 MHz or 3 Mbps?

    At 3 MHz, each cycle is only 333 ns.  This part has a 2 V tpd of 170 ns (for the 54 version shown on your schematic).  That could certainly cause problems if signals are out of alignment because of the delay.

    The best thing you could do is get oscilloscope shots of the affected input/output pairs to see exactly what is happening.

  • 0 in reply to Emrys Maier
    Expert 2310 points

    Hello,

    I found the problem, that was my fault. In connecting the 4 SPI ports signals on the buffers, I also connected the MISOs together at the output side, so the sensor's output signal could not be buffered.

    Thanks for your help, anyway.

    Stefano