K-Line – A Component of the Automobile Industry
Modern vehicles, especially many prestige vehicles must have the technical capacity to communicate within their network. The interaction of the participants will make it possible to automate the processes in a system so that faults can be recognized and corrected early. Comfort also plays a role, even when the focus is on the aspect of safety, in addition to the aim of making an automobile more economic and efficient. Buses are being used for decades to meet these demands. Behind a bus stands the Binary Unit System, which is the system serving the desired data transfer between the participants of a network topology via a common transfer path. With this, the participants are not involved in the transfer of messages, telegrams, and files of other participants.
General Information via the K-line
Buses, including the K-line, are used to meet the requirements of industrial communication and information technology. This is a bidirectional single-wire bus serving data transfer between elements of a network in automobile technology. It is defined in the standards ISO 9141 and ISO 14230. The special characteristic of this form of data connection is that this bus can also be operated unidirectionally when the L-line is used in addition to the K-line. On a higher level, this use serves the automation of work steps, but in detail, this function provides the handling of the communication with the outside, stimulation of the control device, and initialization of the corresponding processes.
The single-wire bus
The K-line is a single-wire connection and thus a serial interface, which is directed via a data strand and has a ground connection, so that the designation as a bus with one wire is basically wrong or at least confusing. Accordingly, in practice the K-line has two physical conductor connections being used. Power supply and control of transmission and reception are the main tasks of these technical components. The form of the arrangement is called button-shaped and has the advantage that this structure is a simple factor for authentication. A single-wire bus, and thus also the K-line, has the following characteristics:
- The connection is serial and operates over one data line each for transmission and reception. This is called bidirectional.
- The transfer of data is done without a clock signal and thus is asynchronous.
- The process is used for transmission is a half-duplex process, so that a block can be received or sent, but both processes never occur at the same time.
- It is a one master/multiple slave system, so that there is only one control unit, but up to 100 sensors or memories exist.
- Each slave has its own 64-bit address.
- The slaves require no external voltage supply, as there is an internal capacitor.
- The single-wire bus is a voltage interface.
Establishing Communication with the K-line
For initialization of establishment of communication between the participants in a network, there must first be stimulation. This takes place between the control unit and the respective external diagnosis computer. This stimulation can take place in two different forms:
- Fast initialization – here the communication is established via the low level, as the logical 0 is held for a short duration. Then the normal interaction starts.
- 5-baud initialization – in order to obtain a connection between the control unit and the diagnosis computer in this case, extremely slow telegram bytes are sent, which have the task of breaching the parity condition. As soon as the stimulation phase ends, normal fast communication occurs.
As in the case of other buses, the K-line uses a certain protocol for structuring of the process and its style during communication. In this case, normally the KWP, the keyword protocol, is used, a communication protocol working with keywords. The advantage of the KWP is the ability to use the diagnosis connection to overwrite the firmware with better developed software versions.
The Future of the K-line
Although the bus uses a form of data transfer that can never occur in both directions, the definition of the bus is maintained, as several control units communicate via one and the same cable. Accordingly, the K-line is still a basic component of the sector of automation technology, but by now this single-wire bus is being increasingly replaced by more modern buses. Because of the dependency of modern vehicles on the exhaust gas standard, it is almost certain that the K-line will no longer be used, but will have tobe replaced by the CAN bus, as this is more efficient and effective in regard to the exhaust gas standard.