JAJSLQ5C April 2021 – September 2022 ADS127L11
PRODUCTION DATA
The read register command is used to read register data. The command follows an off-frame protocol in which the read command is sent in one frame and the ADC responds with register data in the next frame. The first byte of the command is the base command value (40h) added to the 4-bit register address. The value of the second command byte is arbitrary, but is used together with the first byte for the CRC. The response to registers outside the valid address range is 00h. The register data format is most-significant-bit first.
Figure 8-29 shows an example of reading register data using the 16-bit output frame size. Frame 1 is the command frame and frame 2 is the data response frame. The frames are delimited by taking CS high. The data response frame is padded with 00h after the register data byte to fill the 16-bit frame. If desired, the data response frame can be shortened after the data byte by taking CS high.
If operating in full-duplex mode (such as a simultaneous read of 24-bit conversion data during the input of the register read command), pad the command frame with a leading 00h value to match the length of the data response frame. When configuring multiple registers, full-duplex operation can be used to double the throughput of the read register operations by inputting the next read register command during the data response frame of the previous register.
Figure 8-30 shows an example of the read register operation using the maximum 40-bit frame size in full-duplex operation. In frame 1, conversion data are output at the same time as the input of the read register command (if the previous frame was not a read register command). The input command is padded with two don't care bytes in order to match the length of the output data frame. The padded input bytes are excluded from the CRC-IN code calculation. Frame 2 shows the input of the next read register command concurrent with the output of the previous register data. Zeros are padded after the register data to place CRC-OUT in the same location as with a conversion data output frame. The CRC-OUT code includes all preceding bytes within the data output frame. The SPI_ERR bit of the STATUS header indicates if an SPI CRC error occurred and whether the read register command is accepted.