TC1796
Peripheral Units (Vol. 2 of 2)
Controller Area Network (MultiCAN) Controller
User’s Manual 22-44 V2.0, 2007-07
MultiCAN, V2.0
22.3.10 Message Object Data Handling
22.3.10.1 Frame Reception
After the reception of a message, it is stored in a message object according to the
scheme shown in Figure 22-19. The MultiCAN module not only copies the received data
into the message object, and it provides advanced features to enable consistent data
exchange between MultiCAN and CPU.
MSGVAL
Bit MSGVAL (Message Valid) in the Message Object n Status Register MOSTATn is the
main switch of the message object. During the frame reception, information is stored in
the message object only when MSGVAL = 1. If bit MSGVAL is cleared by the CPU, the
MultiCAN module stops all ongoing write accesses to the message object. Now the
message object can be re-configured by the CPU with subsequent write accesses to it
without being disturbed by the MultiCAN.
RTSEL
When the CPU re-configures a message object during CAN operation (for example
clears MSGVAL, modifies the message object and sets MSGVAL again), the following
scenario can occur:
1. The message object wins receive acceptance filtering.
2. The CPU clears MSGVAL to re-configure the message object.
3. The CPU sets MSGVAL again after re-configuration.
4. The end of the received frame is reached. As MSGVAL is set, the received data is
stored in the message object, a message interrupt request is generated, gateway and
FIFO actions are processed etc.
After the re-configuration of the message object (after step 3 above) the storage of
further received data may be undesirable. This can be achieved through bit
MOCTRn.RTSEL (Receive/Transmit Selected) that makes it possible to disconnect a
message object from an ongoing frame reception.
When a message object wins the receive acceptance filtering, its RTSEL bit is set by the
MultiCAN module to indicate an upcoming frame delivery. The MultiCAN module checks
RTSEL whether it is set on successful frame reception to verify that the object is still
ready for receiving the frame. The received frame is then stored in the message object
(along with all subsequent actions such as message interrupts, FIFO & gateway actions,
flag updates) only if RTSEL = 1.
When a message object is invalidated during CAN operation (clearing bit MSGVAL),
RTSEL should be cleared before setting MSGVAL again (latest with the same write
access that sets MSGVAL) to prevent the storage of a frame that belongs to the old
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