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4 Functional description
The BiSS C protocol enables simultaneous transmission of sensor data (SD) from slave to master and
control data from master to slave.
4.1
The BiSS-Frame
The isochronous transmission of the BiSS frames is typically used for cyclical scanning systems. Here, each
cycle begins with the transmission of a BiSS frame, the interface remains in the idle state up to the beginning
of the next cycle. The cycle duration is therefore at least equal to the duration of a BiSS frame, and may be
as long as desired.
Figure 2
In each BiSS frame, one bit of control data (CD) is transmitted per direction for the command or for register
communication. The control data bit of the masters (CDM, Control Data Master) is sent to all slaves via the
line MA as an inverse signal level of the BiSS timeout.
The addressed slave responds with the CDS (Control Data Slave) bit which is always transmitted in the first
bit after the start bit. The control data bits of several consecutive BiSS frames are combined by the master
and by the slaves to form a control frame. It permits the reading and writing of the slave register and the
sending of commands to the slave.
4.2
Processing time per request
If a slave requires additional processing time before outputting its sensor data, e.g. for A/D conversion or for
memory access, it can request this by delaying the start bit. The master detects the delayed start bit and
generates the additionally required MA clock pulses.
Figure 3
4.3
Bus reset
After switch-on or an error, the master must maintain a break of 40 μs prior to the data transmission. This
ensures that the BiSS timeout has expired and all slaves are ready for data transmission.
