SPI communication on the AMC131M01 is performed in frames. Each SPI communication frame consists of several words. The word size is configurable as either 16, 24, or 32 bits by programming the WLENGTH[1:0] bits in the MODE register.

The interface is full duplex, meaning that the interface is capable of transmitting data on DOUT while simultaneously receiving data on DIN. The input frame that the host sends on DIN always begins with a command. The first word on the output frame that the device transmits on DOUT always begins with the response to the command that was sent in the previous input frame.

The number of words in a command depends on the command provided. For most commands, there are three words in a frame. On DIN, the host provides the command, the command CRC if input CRC is enabled or a word of zeros if input CRC is disabled, and one additional word of zeros. Simultaneously on DOUT, the device outputs the response from the previous frame command, one word of ADC data representing the single ADC channel, and a CRC word. If The ADC is disabled, this frame structure of three words still applies, and the data of the disabled channel reads all zeros. Figure 8-19 shows a typical command frame structure.

Figure 8-19 Typical Communication Frame

There are some commands that require more than three words. In the case of a read register (RREG) command where multiple registers are read, the response to the command contains the acknowledgment of the command followed by the register contents requested, which can require a larger frame depending on how many registers are read. See the RREG section for more details on the RREG command.

In the case of a write register (WREG) command where multiple registers are written, the frame extends to accommodate the additional data. See the WREG section for more details on the WREG command.

See the Commands section for a list of all valid commands and the corresponding responses on the AMC131M01.

Under special circumstances, a data frame can be shortened by the host. See the Short SPI Frames section for more information about artificially shortening communication frames.