Analog Devices MAX96752 User Manual page 34

State of RO (Read Only) pin dictates direction of data movement.
• RO = 0: Data transmitted between main and subordinate via MOSI
• RO = 1: Data transmitted between subordinate and main via MISO, BNE will be high if there are bytes in this buffer
to be read back.
Note that the word "read" in the name of the RO pin does not mean that it is an output pin; it is, in fact, an input pin
that is toggled externally high or low depending on read or write operation.
It is recommended to limit the amount of "bytes in transit" (bytes that have been sent but not received back) to 16.
The external SPI main device can compute this value (= valid bytes sent – valid bytes read).
One way of doing this is to send the data in a group of 16 bytes or less. If more than 16 bytes are sent at a time, it is
still possible (depending on timing) that all the data will be sent properly, but it will not be possible to easily be
sure that the data was sent properly.
Below is an example of transferring 4 bytes of SPI data across the GMSL link:
• RO is pulled high, and the A0 and A4 control commands are sent.
• RO is pulled low, and 4 bytes of SPI data (0x80, 0x04, 0x01, 0x47) are sent from the external SPI main device to
the GMSL input side (serializer).
• The last three signals in the graph show SPI data output from the remote side of the link (deserializer), there
may be some delay between the input and output of the SPI data across the GMSL link.
• RO is high, and the bytes are read back by the external SPI main device (BNE is high, which indicates that SPI
data bytes from the external SPI subordinate are available to be read.).
Each Rx and Tx SPI buffer has overflow detection logic with status bits that can be monitored by registers
SPI_TX_OVRFLW and SPI_RX_OVRFLW.
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Figure 22. SPI Transmission Example
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