wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

45-8 Industrial Communication Systems
The two parity bits for the ID are calculated using the following equations:
P0 = ID0 ⊕ ID1⊕ ID2 ⊕ ID4
(45.2)
P1 = ID1⊕ ID3 ⊕ ID4 ⊕ ID5 (45.3)
45.5.4 Data Field
The data field is the first part of the response. The response can also be generated in the master by the
slave task and can consist of one to eight data bytes. As described above, the ID determines the number
of bytes unless another length is indicated. The signals are transmitted in the data bytes, starting with
the least significant bit (LSB). A data byte consists of a start bit, eight data bits, and a stop bit. A parity
bit is not transferred.
45.5.5 Checksum
There is a distinction in LIN between a so-called classic checksum and an enhanced checksum. The
LIN protocol version 1.3 uses the classic checksum. LIN version 2.x uses the enhanced checksum and
includes the PID. The enhanced checksum is only used for the IDs 0x0–0x3B (0–59).
45.5.6 Frame Length
The minimum and the maximum header and frame length are specified in the LIN specification. The
maximum values are 140% of the minimal times. An under run of the minimum times is not possible
because they exactly correspond to at least the necessary bit times. Table 45.3 summarizes these
parameters.
45.5.7 time-Triggered Data Transmission
Modern automotive networking solutions favor the time-triggered model for message scheduling so
that the overall timing of messages in the system can be deterministic. In a time-triggered network,
messages are transmitted against a predefined message schedule table and there is a notion of a global
clock to ensure proper time synchronization. The FlexRay network is an example of such an automotive
time-triggered network. Since LIN is a subnetwork that can be used in conjunction with larger networks
in a system, LIN supports time-triggered operations.
LIN controls the time-triggered transmission by using schedule tables, which are implemented in
the master. Thus, the system can be deterministic, that is, the time when a message is transmitted can
be exactly predicted and guarantees the periodicity of signals. The schedule tables define a time slot for
every scheduled frame, as are described in the LDF by the system designer.
Table 45.3 Nominal and Maximum
Transmission Time of Headers and Frames
Name
T Header_Nominal
T Response_Nominal
T Frame_Nominal
T Header_Maximum
T Response_Maximum
T Frame_Maximum
34 T Bit
10*(N Data + 1) T Bit
T Header_Nominal + T Response_Nominal
1.4*T Header_Nominal
1.4*T Response_Nominal
T Header_Maximum + T Response_Maximum
© 2011 by Taylor and Francis Group, LLC