PRECESSION ELEPHANT 2 Scan Head 2
HSSI data transfer protocol
Scan head and controller communicate via the HSSI data transfer protocol based on the
S/PDIF protocol.
In order to code the digital signals the Biphasic Mark Code (BMC) is used. The BMC is a
kind of phase modulation, where 2 signal zero-crossings correspond to a logical "1" and
1 signal zero-crossing correspond a logical "0".
The following table shows the allowed bit rates and the resulting sub frames.
Bit rate
Sub frames Update rate per channel
6.144 Mb/s 192000/s
48 kHz (factory setting)
12.288 Mb/s 384000/s
96 kHz (optional for IDB416-30 or higher)
The clock frequency is twice the bit rate. In a Biphasic Mark signal each bit of the
original signal is composed of 2 logical states which represent a so called cell. The
length of a cell corresponds to the length of a data bit. The logical state at the
beginning of a cell is always the inverted state of the previous cell. The logical state at
the ending of a cell either will be inverted (if a logical "1" is transmitted in the original
signal) or levels off (if a logical "0" is transmitted in the original signal).
The following figure shows an example.
94
