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TouCAN Architecture
16.3.1.2 Fields for Extended Format Frames
Table 16-4 describes the message buffer fields used only for extended identifier format
frames.
Field
ID[28:18]/[17:15]
Contains the 14 most significant bits of the extended identifier, located in the ID_HIGH word
of the message buffer.
Substitute Remote
Contains a fixed recessive bit, used only in extended format. Should be set to one for Tx
Request (SRR)
buffers. It will be stored as received on the CAN bus for Rx buffers.
ID Extended (IDE)
If extended format frame is used, this field should be set to one. If zero, standard format frame
should be used.
ID[14:0]
Bits [14:0] of the extended identifier, located in the ID_LOW word of the message buffer.
Remote Transmission
This bit is located in the least significant bit of the ID_LOW word of the message buffer
Request (RTR)
0 Data Frame
1 Remote Frame
16.3.1.3 Fields for Standard Format Frames
Table 16-5 describes the message buffer fields used only for standard identifier format
frames.
Field
16-bit Time Stamp The ID_LOW word, which is not needed for standard format, is used in a standard format buffer
to store the 16-bit value of the free-running timer which is captured at the beginning of the identifier
field of the frame on the CAN bus.
ID[28:18]
Contains bits [28:18] of the identifier, located in the ID_HIGH word of the message buffer. The four
least significant bits in this register (corresponding to the IDE bit and ID[17:15] for an extended
identifier message) must all be written as logic zeros to ensure proper operation of the TouCAN.
RTR
This bit is located in the ID_HIGH word of the message buffer;
0 = data frame, 1 = remote frame.
RTR/SRR Bit
If the TouCAN transmits this bit as a one and receives it as a zero, an "arbitration loss" is
Treatment
indicated. If the TouCAN transmits this bit as a zero and receives it as a one, a bit error is
indicated.
If the TouCAN transmits a value and receives a matching response, a successful bit transmission
is indicated.
16.3.1.4 Serial Message Buffers
To allow double buffering of messages, the TouCAN has two shadow buffers called serial
message buffers. The TouCAN uses these two buffers for buffering both received messages
and messages to be transmitted. Only one serial message buffer is active at a time, and its
function depends upon the operation of the TouCAN at that time. These buffers are not
accessible or visible to the user.
16-6
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
Table 16-4. Extended Format Frames
Table 16-5. Standard Format Frames
MPC533 Reference Manual
Description
Description
MOTOROLA
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