MC68F375
CAN 2.0B CONTROLLER MODULE
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
7-16
7.5.5 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, the user initializes a message buffer as a transmit mes-
sage 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.
7.5.6 Overload Frames
The TouCAN does not initiate overload frame transmissions unless it detects the fol-
lowing conditions on the CAN bus:
A dominant bit in the first or second bit of intermission.
A dominant bit in the seventh (last) bit of the end-of-frame (EOF) field in receive
frames
A dominant bit in the eighth (last) bit of the error frame delimiter or overload frame
delimiter
7.6 Special Operating Modes
The TouCAN module has three special operating modes:
Debug mode
Low-power stop mode
Auto-power save mode
7.6.1 Debug Mode
Debug mode is entered when the FRZ1 bit in CANMCR is set and one of the following
events occurs:
The HALT bit in the CANMCR is set; or
The IMB3 FREEZE line is asserted
Once entry into debug mode is requested, the TouCAN waits until an intermission or
idle condition exists on the CAN bus, or until the TouCAN enters the error passive or
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Freescale Semiconductor, Inc.
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