The SYNC command can be thought of as a reset of the digital filter paths and logic within the AD777x. One of the major events that the sync triggers is the reloading of the digital filter coefficients based on the selected configuration. A SYNC should be provided to the AD777x after any changes to the AD777x configuration, before valid samples are acquired..
If a SYNC is not provided after a configuration change, then, for example, the digital filter coefficients used may not be correct for that configuration. In this case, an unexpected filter profile could be used, until a SYNC is provided.
The sync signal can be provided direct to the AD777x SYNC_IN pin, to the START pin, or can be triggered over SPI, under SPI mode control. To provide the SYNC over SPI or through the START pin, the SYNC_OUT and SYNC_IN pins must be tied together.
Once the SYNC is provided, it is no longer required to provide a SYNC again, until either the part is reset, or the configuration is changed.
The SYNC command is also required to synchronize multiple devices. For more information related to how to synchronize devices, please refer to: Newest Sigma-Delta ADC Architecture Averts Disrupted Data Flow When Synchronizing Critical Distributed Systems | Analog Devices
The RESET command causes a full reset of the AD777x, and the device is set to its default configuration, so the register values previously configured will be lost (gain, offsets…). It is useful to put the AD777x into a known valid configuration, with all internal registers set to default values after the power up because a slow slew rate in the supplies may generate an incorrect initialization in the digital block.
Some of the default parameters are as follows:
- Sinc3 digital filter enabled.
- Analog input precharge buffers are enabled on all channels.
- The offset, gain, and phase calibration registers are reset to the factory settings.
- Internal reference buffer disabled by default.
- SAR ADC disabled.