XC886/888CLM
Bootstrap Loader
User’s Manual
18-29
V1.3, 2010-02
Bootstrap Loader, V1.0
18.2
MultiCAN BSL Mode
MultiCAN BSL can be entered only when Flash is not protected, else user mode is
entered instead and code from memory address location 0000
H
will be executed. The
MultiCAN BSL protocol is divided into two sections, hardware initialisation and software
communication.
In the hardware initialisation section, XC886/888 is configured to use an external
oscillator and CAN node 0 for communication. The use of external oscillator is to ensure
an optimal performance on CAN applications, which requires the oscillator to have a
frequency deviation of less than 1.5 %. XC886/888 supports four oscillator frequency
values, which the user can enter at the top address of the P-Flash banks. The usage for
user defined parameter is described in
In the software communication section, three main phases have been identified, namely
the Autobaud, Acknowledgement and Data Reception phases. All three phases involves
the transmission and reception of CAN Message Objects
1)
.
The Autobaud phase is started on entry to MultiCAN BSL where the host sends a Host
Command Message to the microcontroller. The microcontroller will determine the current
CAN network baud rate and configure the baud rate of the CAN node accordingly to
enable the communication channel. In the Acknowledgement Phase, the microcontroller
sends an Acknowledge Message to the host to establish the communication channel.
With the communication channel established, the Data Reception Phase can now be
started. The host sends Data Message Objects to download the code into XRAM and
execute the code from there. In the XC886/888, there are 1.5 Kbytes of XRAM available
for program execution.
The following assumptions are introduced to keep the MultiCAN BSL implementation
simple:
•
Host and the XC886/888 are the only CAN node in the CAN network (Point to Point
Connection)
•
CAN Node 0 (P1.0/P1.1) on the XC886/888 is used for this mode
•
XC886/888 expects to receive a standard CAN frame with message identifier of
555
H
.
18.2.1
Communication protocol
Data is exchanged using Message Objects implemented with the standard CAN data
frame (11 bit identifier) as shown in
. Message Objects with other message
identifiers are ignored by XC886/888. The data field in a standard CAN message is used
to implement the communication protocol.
1) CAN Message Object refers to a standard CAN data frame as defined in BOSCH CAN Specification 2.0B
*
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