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Original question:

PGA970: SPI communication mode selection issue

PGA970: PGA970QPHPR

Nicholas Emerson
Prodigy 30 points
Part Number: PGA970

Few questions:

1. SPI comms:

     The data sheet says 

1. When comparing the VIH and VIL parameters we see that "MOSI and MISO" are used in both. Can someone please confirm this is a matter of perspective? As in the PGA970 could be operated as a master or a slave - I know later on in the datasheet pg 41 states that the PGA970 can only operate as a slave... so what gives?

2. Why does the VOH and VOL not call out "MOSI or MISO" ? 

Waveform Excitation Voltage:

My 4-wire LVDT has a sensitivity of 0.044V/mm/Vex when the excitation voltage is 2.3 Vrms at 5 kHz. I cannot tell through the data sheet if the PGA970 waveform generator is capable of this?

  • 0
    TI__Guru** 113765 points

    Hi Nicholas,

    Welcome to the E2E forum!

    Nicholas Emerson said:

    1. SPI comms:

         The data sheet says 

    1. When comparing the VIH and VIL parameters we see that "MOSI and MISO" are used in both. Can someone please confirm this is a matter of perspective? As in the PGA970 could be operated as a master or a slave - I know later on in the datasheet pg 41 states that the PGA970 can only operate as a slave... so what gives?

    The PGA970 communicates as SPI slave only.  It cannot be a SPI master.  I agree that the datasheet could be more clear regarding the SPI operation and unfortunately cannot give you a good answer as to why MISO is listed in the VIH and VIL parameters.  I will make note of this to be fixed in a future datasheet update.

    Nicholas Emerson said:
    2. Why does the VOH and VOL not call out "MOSI or MISO" ? 

    This is the actually correct as the only output pin is MISO.

    Nicholas Emerson said:
    My 4-wire LVDT has a sensitivity of 0.044V/mm/Vex when the excitation voltage is 2.3 Vrms at 5 kHz. I cannot tell through the data sheet if the PGA970 waveform generator is capable of this?

    In the single-ended output case no, but should work in differential output.  You will be limited by the DAC output (1.25V max) and gain settings (1.67V max).  This may be more followed by reviewing information in the PGA970EVM user's guide in section 3 and reviewing the schematic.  The EVM includes an example on how to increase the output using amplifiers.

    Best regards,

    Bob B