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Original question:

TXU0304: Clarification on the SPI pins

TXU0304: TXU0304

Manmohan garg
Prodigy 20 points
Part Number: TXU0304
Other Parts Discussed in Thread: SN74LVC125A, SN74LVC244A

Hi,

I need to use SPI master/slave configuration, have one STM32 as master uC as SPI master & 6 STM32 are slaves, i was trying on one prototype which involved external wiring, bus without repeater, facing issues in SPI communication, it can work for lower frequency less than 400kHZ, then i thought to use bus repeater, if I use TXU0304 for all 4 signals(MISO/MOSI/CS/CLK),which way is correct, one TXU0304 is for one slave(means total 6 TXU0304- input is common & output is dedicated to each slave) or I can use only one TXU0304 for all 6 slaves, Please advice which is the best methodology.

Thankyou.

Manmohan

  • 0
    Guru 277260 points

    If the voltages are the same, then you can use plain buffers (e.g., SN74LVC125A, SN74LVC244A).

    How many buffers to use depends on the length of the wiring they need to drive. When in doubt, use separate ones.

    Please note that the MISO lines can be connected together only if you ensure that inactive slaves do not drive it. This is normal for actual SPI devices, but it is likely that you must connect the respective /CS to /OE for the buffers.

  • 0 in reply to Clemens Ladisch
    Prodigy 20 points

    Thanks Clemens!!

    SPI bus length is more than 50cm, Going to use same voltage on both sides, I want to use this for communication on high speed, without any buffer i am facing issues on clk frequency more than 500Khz. not sure whether plain buffer will be ok for Hi-speed like 10Mhz or more.

    i have one application in which 6 slaves,in other application 12 slaves are there, definitely I am going to use one slave at a time using CS/OE control.

  • 0 in reply to Manmohan garg
    Guru 277260 points

    Check the voltages with an oscilloscope. If there are reflections at the edges, add proper termination (the easiest is source termination, i.e., a resistor of about 22 Ω … 33 Ω at the driver). If the clock line picks up noise, you would need shielding, or you would have to use a differential protocol like LVDS.

  • 0 in reply to Clemens Ladisch
    Prodigy 20 points

    Thanks Clemens!! I think now I got it.