Is a hardware reset required before each calibration of the AD7172-2 ?
No it is not required. But as a good practice upon initialization it is recommended to reset the part upon power up, by applying a number of 64 consecutive ones to the interface. This will ensure that all registers are set to their default values before configuring the device including performing calibrations.
When using the AD7172-2, the calibration can only be performed after power-up. If the calibration is performed after reading the data value of the data register, the value of the ADC data register cannot be read. When reading the value of the data register, the program is stuck in the SPI data receiving stage .The configuration of other registers is the same as the configuration when the device is initialized. Please, what is the possible reason?
The calibration can be performed any time by writing the relevant value to the mode register. However, please take note the calibration procedure mentioned in page 40 must be followed. Please take note also that after performing calibrations the part will revert to standby mode. Can you try to change the mode back to continuous conversion mode for example and see if the issue is still there?