Take special precaution when collecting data for the first time or when beginning to collect data again after a pause. The internal mechanism that outputs data contains a first-in-first-out (FIFO) buffer that can store two samples of data per channel at a time. The DRDY flag for each channel in the STATUS register remains set until both samples for each channel are read from the device. This condition is not obvious under normal circumstances when the host is reading each consecutive sample from the device. In that case, the samples are cleared from the device each time new data are generated so the DRDY flag for each channel in the STATUS register is cleared with each read. However, both slots of the FIFO are full if a sample is missed or if data are not read for a period of time. Either strobe the SYNC/RESET pin to re-synchronize conversions and clear the FIFOs, or quickly read two data packets when data are read for the first time or after a gap in reading data. This process ensures predictable DRDY pin behavior. See the Section 8.5.2 section for information about the synchronization feature. These methods do not need to be employed if each channel data was read for each output data period from when the ADC was enabled.

Figure 8-20 depicts an example of how to collect data after a period of the ADC running, but where no data are being retrieved. In this instance, the SYNC/RESET pin is used to clear the internal FIFOs and realign the ADS131M04-Q1 output data with the host.

Figure 8-20 Collecting Data After a Pause in Data Collection Using the SYNC/RESET Pin

Another functionally equivalent method for clearing the FIFO after a pause in collecting data is to begin by reading two samples in quick succession. Figure 8-21 depicts this method. This example shows when the DRDY_FMT bit in the MODE register is set to 0b indicating DRDY is a level output. There is a very narrow pulse on DRDY immediately after the first set of data are shifted out of the device. This pulse may be too narrow for some microcontrollers to detect. Therefore, do not rely upon this pulse but instead immediately read out the second data set after the first data set. The host operates synchronous to the device after the second word is read from the device.

Figure 8-21 Collecting Data After a Pause in Data Collection by Reading Data Twice