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Special Operating Modes
16.4.5
Remote Frames
The remote frame is a message frame that is transmitted to request a data frame. The
TouCAN can be configured to transmit a data frame automatically in response to a remote
frame, or to transmit a remote frame and then wait for the responding data frame to be
received.
To transmit a remote frame, a message buffer is initialized as a transmit message buffer with
the RTR bit set to one. Once this remote frame is transmitted successfully, the transmit
message buffer automatically becomes a receive message buffer, with the same ID as the
remote frame that was transmitted.
When the TouCAN receives a remote frame, it compares the remote frame ID to the IDs of
all transmit message buffers programmed with a code of 1010. If there is an exact matching
ID, the data frame in that message buffer is transmitted. If the RTR bit in the matching
transmit message buffer is set, the TouCAN transmits a remote frame as a response.
A received remote frame is not stored in a receive message buffer. It is only used to trigger
the automatic transmission of a frame in response. The mask registers are not used in
remote frame ID matching. All ID bits (except RTR) of the incoming received frame must
match for the remote frame to trigger a response transmission.
16.4.6
Overload Frames
The TouCAN does not initiate overload frame transmissions unless it detects the following
conditions on the CAN bus:
• A dominant bit is the first or second bit of intermission
• A dominant bit is the seventh (last) bit of the end-of-frame (EOF) field in receive
frames
• A dominant bit is the eighth (last) bit of the error frame delimiter or overload frame
delimiter
16.5 Special Operating Modes
The TouCAN module has three special operating modes:
• Debug mode
• Low-power stop mode
• Auto power save mode
16-18
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
MPC533 Reference Manual
MOTOROLA
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