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TC1796
Peripheral Units (Vol. 2 of 2)
Controller Area Network (MultiCAN) Controller
User’s Manual
22-150
V2.0, 2007-07
MultiCAN, V2.0
transfers of reference messages, the external trigger generation should be switched off
in this case.
22.7.5
Error Handling
The TTCAN error handling distinguishes among four levels of error severity:
•
S0:
No Error: Normal functionality
•
S1:
Warning: Only notification of the application by an interrupt (ERRS1).
Source: Scheduling Error 1 (MSCmax - MSCmin > 2 or when MSC of a receive
object equal 7), Tx_Underflow
•
S2:
Error: Notification of the application by an interrupt (ERRS2). All transmissions are
disabled (except for reference messages), TTCFGR.RTO is set to 127.
Source: Scheduling Error 2 (MSC of a transmit object reaches 7), Tx_overflow
Impact: The transmit enable window will not be opened (for exclusive and for
arbitration windows).
•
S3:
Severe Error: Notification of the application by an interrupt (ERRS3). All CAN bus
actions are stopped (no dominant values are transmitted on the bus). The
configuration phase is entered automatically (CFGM is set).
Source: Application Watchdog, Bus Off, Config Error, Watch Trigger Event
Impact: Bit INIT of the CAN node will be set (the CAN node stops actions on the bus).
Note: Any change of the error state can generate an interrupt.
22.7.6
Application Watchdog
The application watchdog provides the possibility of checking for the TTCAN module if
the main system is still running. The application watchdog counter counts in steps of
256 NTUs.
Each time 256 NTUs have elapsed, the value AWDR.AWDV is decremented by one. If
the value 0 is reached after decrementing, an S3 error is signaled by bit AWDERR. The
falling edge of bit LTR.LT.7 (transition from 1 to 0) indicates that the time of 256 NTUs
has elapsed and the application watch dog value is decremented.
The application watchdog is serviced by the program by writing a new value to the bit
field AWDR.AWDE.