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TC1796
System Units (Vol. 1 of 2)
Reset and Boot Operation
User’s Manual
4-28
V2.0, 2007-07
Reset, V2.0
4.4.3
Bootstrap Loader Mode 3 - ASC Boot via CAN Pins
Except for different connections to serial port lines of ASC0, the bootstrap loader mode
3 is identical with bootstrap loader mode 1. The serial data input of the ASC0 is
connected to RXD0B which is an alternate function of P6.8/RXDCAN0 and the serial
data output of the ASC0 is connected to TXD0B which is an alternate function of
P6.9/TXDCAN0.
4.4.4
Alternate Boot Modes
The alternate boot modes (ABM) make it possible to execute a CRC check procedure
before jumping to the program start addresses in internal PFLASH or external memory
(with EBU as master or as participant). In case of a CRC error in the checked code, the
BSL is entered, and loading of serial (ASC or CAN) code/data can be initiated.
To use ABMs, the user has to define the parameters for the CRC checks in the two ABM
headers. These parameters are:
•
The program start address in case of a positive CRC check
•
The start address of the memory range which has to be checked with CRC checksum
•
The end address of the memory range which has to be checked with CRC checksum
•
The checksums for the checked memory range and for the ABM header itself.
Basically the CRC check procedure of the Boot ROM program consists of three steps:
Step 1:
The first CRC check is executed with the parameters of the primary ABM header.
If the first CRC check passes, the user program is started at the address as defined in
the first word of the primary ABM header.
Step 2:
If the first CRC check of the primary ABM header fails, a second CRC check with
the parameters of the secondary ABM header is performed. If this second CRC check
passes, the user program is started at an alternate start address as defined in the first
word of the secondary ABM header.
Step 3:
If the second CRC check also fails, one of the three BSL modes is entered. The
BSL mode to be used is defined by the content of bit field SCU_SCLIR.SWOPT[2:0].
This bit field contains the state of the Port 0 pins P0.[2:0] that was latched at the last
rising edge of HDRST (further details on SCU_SCLIR see
Table 4-7
ABM Bootstrap Loader Selections
SWOPT[2:0]
Selected ABM Bootstrap Loader Mode
110
B
Bootstrap Loader Mode 1: ASC Boot via ASC0 Pins
101
B
Bootstrap Loader Mode 2: CAN Boot
111
B
1)
Bootstrap Loader Mode 3: ASC Boot via CAN Pins
others
Reserved; do not use these combinations