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Boot Assist Module (BAM)
MPC5644A Microcontroller Reference Manual, Rev. 6
632
Freescale Semiconductor
If a message with 0x11 ID, containing 8 bytes, is received by the CAN controller first, the BAM program
transitions to the Serial CAN Boot sub-mode, disabling eSCI, and reconfiguring the SCI_A_RX pin to its
reset state.
If a message from eSCI is received first, the BAM program transitions to the Serial SCI Boot submode,
disables CAN_A module and configures its pins to their reset state.
Then the BAM program transitions to the serial download protocol execution.
21.5.5.1
CAN controller configuration in the fixed baud rate mode
The CAN controller is configured to operate at a baud rate equal to system frequency divided by 40, using
the standard 11-bit identifier format detailed in CAN 2.0A specification. See
baud rates. Only one message buffer 0 is used for all communications.
The bit timing is configured as shown in
.
Figure 21-7. CAN bit timing
The BAM program ignores CAN errors and all received data is assumed to be good and is echoed out on
the CN_A_TX signal. It is the responsibility of the host computer to compare the “echoes” with the sent
data and restart the process if an error is detected.
21.5.5.2
SCI controller configuration in fixed baud rate mode
The eSCI is configured for 1 start bit, 8 data bits, no parity, 1 stop bit and to operate at a baud rate equal
to system clock divided by 832. See
for examples of baud rates.
The BAM program ignores the eSCI errors: All data received will be assumed to be good and will be
echoed out on the TXD signal. It is the responsibility of the host computer to compare the echoes with the
sent data and restart the process if an error is detected.
21.5.5.3
Serial boot mode download protocol
The download protocol follows four steps:
1. Host sends 64-bit password.
SYNC_SEG
TIME SEGMENT 1
TIME SEGMENT 2
NRZ Signal
1 time quanta
1 Bit Time
7 time quanta
2 time quanta
Transmit Point
Sample Point
Note: 1 Time quanta = 4 System clock periods
Summary of Contents for MPC5644A
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