Further read of the manual reveals that as you said the 256 registers are at one I2C address, and are divided between control registers and EEPROM addresses (two banks of 128 bytes).
The current implementation has the current modes for the encoder:
A. Relative, where the counter keeps the number of steps since last read. Reading it resets the counter to zero. Useful for frequency tuning in our case.
B1. Without limits.
B2. With user defined limits
B2.1. No wrap around, like a potentiometer, hard stops at the limits.
B2.2 With wrap around, goes back to low limit if high limit is exceeded and vice-versa.
The encoder push button events are:
- button down
- button up
- double-press with user selectable double-press interval.
Current consumption is listed at less than 2mA plus LED current if used.
The board mounted PIC controller's program is open source so it can be customized as well.
Very neat IMO.