Figure 7-3 shows the timing diagram for the SPI interface in non-daisy chain
mode. ISO1228 has SPI Mode 0 with Clock Polarity = Inactive Low, Clock Phase =
Rising/Leading Edge. The bit W/Rn (1/0) determines Write or Read operation. Ab is a
7-bit register for read or write. Wb is the 8-bit write data for Write operation and is
ignored for Read operation. Rb is the 8-bit read data from the register addressed by Ab
during Read operation, and should be ignored for Write operation. O8-O1 is the state of
the 8-digital inputs, IN8-IN1 and is always output on SDO in the Address phase.
If SDI is continuously held at Low
(0), the device will treat this as a Read operation from Address 0. Address 0 holds
the state on IN8-IN1 (see SPI Register Map), so in this special case of Read operation the SDO output will
be IN8-IN1 in both Address and Read Phases. For applications that are only
interested in the state of the digital inputs, and do not want to access other
registers for Read/Write, this option may result in a simpler implementation.