Hiperface encoder

How does the 'serial' data channel on a Hiperface encoder work?
Is position value transferered continuously by the serial channel or only at startup of the device?
What position is transfered by the serial channel? I suppose that the sincos channel is much faster then the serial channel can transfer the consecutive position values.
Is the Hiperface encoder powered only by a battery inside, or is it also powered by the drive is this is powered on, so is it recharged when the drive is on?
I heard that also motor data can be transfered by the hiperface encoder, when is this transfered? At powerup?

There might be manufacturer variances, however, for Sick-Stegmann Hyperface devices, the absolute value stored within the encoder is delivered via digital RS-485 parameter interface only at power-up time; after that, the external controller is incrementally using the analog channel circuit sin/cos signals of the encoder.
The absolute position is stored within the encoder's internal EEPROM (I don't believe a battery is being used); since the EEPROM's size is some 1792 bytes, you could theoretically "write it up" with any relevant data you wish to store and then querry it up whenever the proper commands are being sent.