TC1796
System Units (Vol. 1 of 2)
Reset and Boot Operation
User’s Manual
4-25
V2.0, 2007-07
Reset, V2.0
Initialization Phase
As in the ASC boot mode, as first task the CAN bootstrap loader has to determine the
CAN baud rate at which the external host is communicating. This task requires the
external host to send initialization frames continuously to the TC1796. The first two data
bytes of the initialization frame include a 2-byte 5555
H
baud rate detection pattern, an
11-bit (2-byte) identifier ACKID
1)
for the acknowledge frame, a 16-bit data message
count value DMSGC, and an 11-bit (2-byte) identifier DMSGID
frame.
When CAN boot mode is entered, the CAN bootstrap loader program starts measuring
signal pulses at the RXDCAN0 input. After reception and pulse measurements of a
5555
H
bit pattern (data bytes 0 and 1 of the initialization frame), the CAN bootstrap loader
program calculates the CAN baud rate and programs the baud rate registers of the
MultiCAN module. The TC1796 is now ready to receive CAN frames with the baud rate
of the external host.
Acknowledge Phase
In the acknowledge phase, the bootstrap loader waits until it receives the next correctly
recognized initialization frame from the external host, and acknowledges this frame by
generating a dominant bit in its ACK slot. Afterwards, the bootstrap loader transmits an
acknowledge frame back to the external host indicating that it is now ready to receive
Acknowledge
Frame
Identifier
Acknowledge message identifier ACKID as received by
data bytes [3:2] of the initialization frame
DLC = 4
Data length code, 4 bytes transmitted within CAN frame
Data bytes
0/1
Contents of bit-timing register
Data bytes
2/3
Copy of acknowledge identifier from initialization frame
Data frame
Identifier
Data message identifier DMSGID as sent by data bytes
[7:6] of the initialization frame
DLC = 8
Data length code, 8 bytes transmitted within CAN frame
Data bytes
0 to 7
Data bytes, assigned to increasing destination (SPRAM)
addresses
1) The CAN bootstrap loader copies the two identifier bytes received in the initialization frame directly to register
MOAR. Therefore, the respective fields in the initialization frame must contain the intended identifier padded
with two dummy bits at the lower end and extended with bitfields IDE (=0
B
) and PRI (=01
B
) at the upper end.
Table 4-6
CAN Bootstrap Loader Frames
(cont’d)
Frame Type
Parameter
Description