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TC1728
Controller Area Network Controller (MultiCAN)
20.3.7
CAN Node Analysis Features
The chapter describes the CAN node analysis capabilities of the MultiCAN module.
20.3.7.1 Analyze Mode
The CAN Analyze Mode makes it possible to monitor the CAN traffic for each CAN node
individually without affecting the logical state of the CAN bus. The CAN Analyze Mode
for CAN node x is selected by setting Node x Control Register bit NCRx.CALM.
In CAN Analyze Mode, the transmit pin of a CAN node is held at a recessive level
permanently. The CAN node may receive frames (Data, Remote, and Error Frames) but
is not allowed to transmit. Received Data/Remote Frames are not acknowledged (i.e.
acknowledge slot is sent recessive) but will be received and stored in matching message
objects as long as there is any other node that acknowledges the frame. The complete
message object functionality is available, but no transmit request will be executed.
20.3.7.2 Loop-Back Mode
The MultiCAN module provides a Loop-Back Mode to enable an in-system test of the
MultiCAN module as well as the development of CAN driver software without access to
an external CAN bus.
The loop-back feature consists of an internal CAN bus (inside the MultiCAN module) and
a bus select switch for each CAN node (see
Figure
20-13). With the switch, each CAN
node can be connected either to the internal CAN bus (Loop-Back Mode activated) or
the external CAN bus, respectively to transmit and receive pins (normal operation). The
CAN bus that is not currently selected is driven recessive; this means the transmit pin is
held at 1, and the receive pin is ignored by the CAN nodes that are in Loop-Back Mode.
The Loop-Back Mode is selected for CAN node x by setting the Node x Port Control
Register bit NPCRx.LBM. All CAN nodes that are in Loop-Back Mode may communicate
together via the internal CAN bus without affecting the normal operation of the other CAN
nodes that are not in Loop-Back Mode.
User's Manual
20-32
V1.0, 2011-12
MultiCAN, V2.24
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