Notes on Schedule tables in LIN protocol

One of key properties of LIN protocol is Schedule Tables. It’s applied for managing the timing of frame slots and traffic control on the bus. The application of Schedule Tables in LIN protocol guarantees that LIN bus won’t be overloaded.

To understand schedule tables, the first step you have to do is to clarify the concept of Time Base. For a specifically implemented LIN system, it’s a constant. It’s used to calculate the time length of a frame slot according to the formula T_{frame_slot} = T_base * n, in which n is different for each frame slot. It depends on the length of a frame slot.

A schedule table can incorporate more than one frame slot as shown in Fig. 1. If only one schedule table is present in a system. When it reaches the end of the schedule table, the schedule will go back to the start of the schedule table and continue performing along the sequence in the schedule table.

Fig. 1 Master uses a schedule table

It’s possible that several schedule tables co-exist in a LIN system as shown in Fig. 2. When a schedule table has been performed, any one of the rest of schedule tables may be performed. It depends on system policies.

Fig. 2 Master uses different schedule tables

The inter-frame space is specified in schedule tables. It can’t be negative since there is no arbitration in LIN protocol frame errors will occur. It’s the key factor in schedule table to control transmission timing on the bus as shown in Fig. 3.

Fig. 3 The structure of a frame slot

Note that the inter-frame space points to the space between the end of response of previous frame slot and the start of header of next frame slot. When studying the frame structure as shown in Fig. 4, you’ll find that there is response space between header and response within a frame. The header of master task and the following response of slave task are combined as a full frame slot.

Fig. 4 The structure of a frame