TC1796
Peripheral Units (Vol. 2 of 2)
Controller Area Network (MultiCAN) Controller
User’s Manual
22-117
V2.0, 2007-07
MultiCAN, V2.0
22.5.3.3 Watch Trigger
The watch trigger is used to check if the elapsed time since the last reference message
was received is too long. This is done by comparing the programmed watch trigger value
to the cycle time. This information can generate an interrupt to the system. The watch
trigger value is defined by the scheduler entry for the end of the basic cycle.
22.5.4
Master Reference Mark (Level 2 only)
The time master sends the sum of its reference mark SYNM (integer part) and SYNMFR
(fractional part) and its local offset LOF (integer part) and LOFFR (fractional part) as
master reference mark (MRM), which is stored in the global mark register GMR.
If the master’s clock or its local time has been corrected and a discontinuity has been
introduced, the discontinuity bit DISC is automatically set until the next reference
message is started. The discontinuity bit is set if a write access to LOF or LOFFR occurs.
As a result, the reference message will contain the new reference mark and the
discontinuity bit DISC set for the current time master.
22.5.5
Transmit Enable Window
The transmit enable window determines the number of CAN bit times that may elapse
between the transmit trigger event (time marks in the scheduler) and the real start of the
message on the bus. If this time expires without starting the transmission of the triggered
message, no new transmission attempt will be made in this time window (if it was an
exclusive one or a short arbitration one). The transmit trigger is deleted and an interrupt
may be generated. If the time window is a long, merged arbitration window, the transmit
enable window is not taken into account.