XC886/888CLM
Bootstrap Loader
User’s Manual
18-30
V1.3, 2010-02
Bootstrap Loader, V1.0
Figure 18-6
Standard CAN frame format
Communication is initiated by the host, which continuously sends a Host Command
Message Object until it receives an Acknowledgement Message Object from the
microcontroller.
After the baud rate is determined and the acknowledgement is received by the host, the
host can activate the MultiCAN BSL operational mode by sending the Data Message
Object. All messages received from this point on will have their data bytes sequentially
written into the XRAM starting at location F000
H
. The size of the internal XRAM is 1.5
kbytes which results in a maximum of 1535 8-bit instructions.
Once all messages have been received, the CAN module will be reinitialized. The
bootstrap loader then terminates its sequence and transfers program execution to the
user code by jumping to location F000
H
(i.e. the first loaded instruction). The program
that was loaded into the XRAM from the host will now be executed.
Note: The bootstrap loader assumes all message data is valid. The host should send its
code/data sequentially in multiples of 8 code/data bytes. The user is limited to
sending a maximum of 192 messages.
18.2.2
CAN Message Object definition
Host Command Message Object
In the Autobaud phase, the Host Command message is sent by the host and used for
automatic baud rate detection. Since there are no other nodes (Point-to-Point) on the
bus, the host will continually send the message. The host will transmit this message and
wait for the microcontroller to acknowledge it.
The Host Command message data field contains 8 bytes of information for enabling the
BSL mode. The first 2 data bytes, Byte 0 and 1, contain the value 0x5555. The next 2
data bytes, Bytes 2 and 3, contain the identifier for an acknowledge message that the
microcontroller sends back to the host. Bytes 4 and 5, contain the 16-bit value for the
number of messages to be received. The final 2 data bytes, bytes 6 and 7 contain the
identifier for the data messages that the host will send to the XC886/888 device.
Arbitration Field
(12 bits)
Control
Field
(6 bits)
Data field (0...64 bits)
CRC Field
(16 bits)
Ack
Field
(2 bits)
End of Frame
(7 bits)
Identifier Field
(11 bits)
RTR Bit
(1 bit)
IDE Bit
(1 Bit)
Reserved
(1 Bit)
Data Length
Code
(4 Bits)
CRC Sequence
(15 Bits)
CRC
Delimiter
(1 Bit)
ACK
(1 Bit)
ACK
Delimiter
(1 Bit)
*
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