The data sheet for the ADS8638 doesn't show proper examples of SPI access for configuration writes/reads and for conversion data. By this I mean that we shown a picture of loading the manual and auto scan commands (Figures 86 and 87), which show conversion results, and we are shown a picture of SPI command word access in tables 9 and 10, along with SPI register write and read cycle timing in figures 89 and 90.
But what is not clear is this. Say we configure the device using a SPI command writes to the configuration registers (range, hysteresis for alarms), following the flow chart in figure 93. That flowchart ends with the device staying in the conversion mode, that is, accepting only two commands, manual mode operation register 04 write and auto-mode configuration register 05 write. It also allows the "continue" operation, writing 0s to the DIN pin while clocking out conversion results.
It does not seem like one can write a configuration command to the SPI port once conversion operation starts. I assume this because a register read starts returning requested data from bit 9, and it has to accept a command on the first 8 bits, and it seems like that would stomp on returning conversion results.
So my guess is that to be able to load a new config register, you have to write the Reset Device register (0x01) in place of the continue/manual scan/auto scan) register command. Is this correct?
