Since MAX31865 registers require setting up, it is not possible to use only 3 wires for SPI communication; Two wires are needed for chip select and clock, and the other two are required for setting up the registers and reading data back from MAX31865. However, it is possible if DRDY pin is not used. In this case, the microcontroller should wait maximum conversion time before reading each sample. The maximum conversion time depends on the mode the device is in. Refer to "Temperature Conversion Time" specification in Electrical Characteristics table of the datasheet. Note that in 1-shot mode, initiating each conversion will require writing to the register.
