Communication Protocol

Each stepper motor acts as a "subordinate" module, it listens to all data on the bus, but only responds as long as the message is transmitted without errors and recognizes it's own address.

The M-Bus protocol differs from the CAN and the I/K/P-Busses in that communication takes place within a framework time of 650 microseconds.

When the climate control module (IHKA/R) is commanding a change in position of one or more stepper motors, the sequence of data is:

1. Start bit  - Informs the stepper motors that a command is coming.
2. Synchro bit  - Establishes the message as originating from the IHK control module.
3. Data Field  - The command to move a stepper motor to a particular position.
4. Address Field  - The IHK control unit names the stepper motor the command is intended for.

If the message was received by the stepper motor without error, the stepper motor will carry out the command and transmit it's acknowledgment which is as follows:

1. Synchro Bit  - Establishes the message as originating from the stepper motor
2. Data Field  - Status information from the actuator (feedback)
3. End of Frame  - Closes the communication Session

Communication continues on the M-Bus until the GM send the "go to sleep" command over the K-Bus.