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TC1796
Peripheral Units (Vol. 2 of 2)
Controller Area Network (MultiCAN) Controller
User’s Manual
22-12
V2.0, 2007-07
MultiCAN, V2.0
Figure 22-5 TTCAN Basic Cycle
The structure of the basic cycle is defined once for the whole TTCAN network. Several
different basic cycles are combined to build a matrix cycle or the system matrix. The
sequence of basic cycles in the matrix cycle is controlled by the reference messages.
All possible messages in the TTCAN system are assigned to time windows of the system
matrix. A time window can be:
•
An exclusive time window, in which only one particular message can be transmitted.
•
An arbitrating time window, in which messages can arbitrate for bus access.
•
A free time window, reserved for future extensions.
In exclusive time windows automatic retransmission of messages is disabled. This
guarantees that messages are not delayed by other bus traffic.
22.1.6.3 Global System Time
Level 2 of TTCAN supports a global system time. The time master establishes its own
local time as global time by transmitting reference message. The other CAN nodes in the
network operate as time slaves that calculate their local time offset to the global time by
comparing their local time with the received global time. To compensate for slightly
different clock drifts in the CAN nodes and to provide a consistent view of the global time,
the nodes can perform a drift compensation operation. They compare the length of the
basic cycle in local time to the length of the basic cycle in global time. The difference
(quotient) of the two values gives the adapted TUR.
22.1.6.4 The System Matrix
Typical CAN applications include many control loops and tasks with different periods. All
of them need individual sending patterns for their information. One TTCAN basic cycle
would not offer enough flexibility to satisfy this needs. Therefore, the TTCAN
specification also makes it possible to use more than one basic cycle to build the
communication matrix or system matrix. Several different basic cycles are connected
together to build the matrix cycle. Most combinations of basic cycles are possible, such
MCA05831
Reference
Message
Time
Basic Cycle
Exclusive
Window
Arbitration
Window
Free
Window
Exclusive
Window
Reference
Message
Time Windows