SPI communication on the ADS131B26-Q1 is performed in frames. Each SPI communication frame starts with a CSn falling edge, consists of several words, and ends with a CSn rising edge. The interface is full duplex, meaning that the interface is capable of transmitting data on SDO while simultaneously receiving data on SDI. Figure 9-28 provides an overview of the general SPI frame structure and frame length for the various commands.

The input frame that the host sends on SDI always begins with a command word followed by a command CRC word. The first word on the output frame that the device transmits on SDO always begins with the STATUS word. The number of words in a frame depends on the command provided. See the CommandsCommands section for a list of all valid commands on the ADS131B26-Q1.

For the NULL, RESET, LOCK, UNLOCK, and RREG commands there are six words in a frame. On SDI, the host provides the command, the command CRC, and four additional words of zeros. Simultaneously on SDO, the device outputs the STATUS word, four words of ADC data (representing the data from ADC1A, ADC1B, ADC3A, and ADC3B), and an output CRC word. Figure 9-28 shows a typical communication frame structure. In the remaining sections of this document the SCLK signal is omitted in the figures for clarity.

Figure 9-28 Typical Communication Frame

For a write register (WREG) command where more than three registers are written, the frame extends to accommodate the additional data. See the WREG section for more details on the WREG command.

For a read register (RREG) command, the response to the command in the following frame contains the STATUS word followed by the register data requested, which can require a shorter or longer frame depending on how many registers are read. See the RREG section for more details on the RREG command.