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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.

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.

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

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.

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