1: Is it possible to use toggle mode in i2c interface mode? The final
paragraph in 2 Byte mode states "toggle mode is not supported in 2-byte mode".
This implies that toggle mode is supported in 3 and 4 byte i2c modes.
2: If toggle mode is supported in i2c mode, how do I write to the a and b
registers? Table 20 in the documentation shows a bit that determines whether
register A, or B are being written to. Where/how is the corresponding bit set
in the i2c interface?
This looks like an oversight in the datasheet. Toggle mode is possible in I2C
mode. The MSB of the pointer byte is the A/B bit. Figure 34 of the AD5390
datasheet shows this clearly (relevant for AD5384).