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TMS320F28335: Correct hardware connections to an LM70 temperature sensor using 3-wire spi

Part Number: TMS320F28335
Other Parts Discussed in Thread: LM70

What are the proper hardware connections from the 28335 and the LM70 temperature sensor?  Can the MISO/MOSI be tied directly together on the 28335, or should I add a 10K resistor on the MISO and then tie them together after?  I assume the LM70 has a high impedance on the SI/O line, however isn't stated in the data sheet.  My only concern with the 10K resistor is voltage drop.

  • Hi Kory,

    You can directly connect the SPI lines to controller. No need of external pull-up.

    Regards,
    Gautam
  • Kory,

    You can directly connect the SIMO and SOMI signals together and into the LM70 SI/O pin. Instead of the resistor, you can use the TALK bit to disable the SIMO pin when you want to receive data. Setting SPICTL.TALK to 0, will put SIMO into high-impedance mode, allowing the SI/O pin to drive the line without contention. 

    If the SPI did not have the ability to put the SIMO line into high-impedance mode, then a resistor would induce a small voltage drop allowing the SI/O to overdrive whatever SIMO is driving. 

    I hope this helps!