TC1796
Peripheral Units (Vol. 2 of 2)
Controller Area Network (MultiCAN) Controller
User’s Manual 22-121 V2.0, 2007-07
MultiCAN, V2.0
22.5.8.2 Transmit Trigger for a Reference Message
The transmission of a reference message can be triggered by a time mark or by an
external event. If it is triggered by a time mark, the “Next is Gap” bit (TTSR.NIG) of the
previous reference message has been 0. If it is triggered by an external event, the “Next
is Gap” bit of the previous reference message has been 1.
The software can set bit TTSR.NIG in order to initiate the synchronization of a reference
message to an event. This event can be an edge at an external input or a software action
(write bit TTFMR.STE = 1, software trigger event).
When TTSR.NIG is set, it will be transmitted with the next reference message in order to
indicate the following synchronization gap to the other CAN nodes. The value of
TTSR.NIG is copied to bit TTSR.ETR (external trigger request) and cleared
automatically when the reference message has been correctly transmitted. Bit
TTSR.ETR = 1 indicates that the next reference message will be transferred as soon as
the corresponding time mark is reached (respecting the gap), or when the selected
trigger event (ETREV) is pending. The evaluation of ETREV is not started before 1 CAN
bit time has elapsed after the end of the transmit enable window of the last transfer
window.
The transmit trigger generation logic for the reference message is shown in
Figure 22-29. The edge detection for ECTTx contains a synchronization stage.
The trigger event can be selected by bit field ETESEL (external trigger event selection).
Only trigger events are taken into account for the transfer of a reference message that
have been detected after the start of the current basic cycle.
The edge detection for ECTTx contains a synchronization stage.
The synchronization of more than one TTCAN node to other TTCAN nodes can be
achieved by setting ETESEL = 00
B
. In this case, the trigger of the reference message of
TTCAN nodes 0-7 (TRMCx) is used to trigger the transmission of the reference
message. As a result, the reference messages can be synchronized between several
TTCAN nodes of the MultiCAN/TTCAN. If not all possible TTCAN nodes are
implemented, the TRMCx of not implemented nodes are 0.
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