NXP Semiconductors PXN2020, Reference Manual, Page: 262 / 1376

Boot Assist Module (BAM)
PXN20 Microcontroller Reference Manual, Rev. 1
9-8 Freescale Semiconductor
9.3.3.2 Serial-Boot Mode Features
In this mode of operation, the BAM code configures FlexCAN_A and eSCI_A for serial download of a
user program. Unused message buffers in FlexCAN_A are used for stack and global variables. The system
clock is selected directly from main crystal oscillator output; thus, the crystal frequency defines baud rates
for serial interfaces, used to download the user application.
9.3.3.2.1 FlexCAN and eSCI Configuration
The BAM program configures FlexCAN_A and eSCI_A to receive messages. The CNRX_A and the
RXD_A pads are configured as inputs to the FlexCAN and eSCI modules. The CNTX_A pad is configured
as an output from the FlexCAN module.The TXD_A pad remains configured as GPIO input until a valid
eSCI byte is received before a valid CAN message.
The FlexCAN controller is configured to operate at a baud rate = system clock frequency / 40, using the
standard 11 bit identifier format detailed in CAN 2.0A specification. (See
Table 9-6 for examples of baud
rates.)
The BAM program ignores all possible errors that may happen during the serial communication. All
received data is assumed to be good and is echoed on the CNTX signal.
The CAN controller bit timing is programmed with 10 time quantas and the sample point is two time
quantas before the end (see
Figure 9-5 ).
Offset: BOOT_BLOCK_A 0x0004 Access: User read-only
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
R A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 A15
W
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
R A16 A17 A18 A19 A20 A21 A22 A23 A24 A25 A26 A27 A28 A29 A30 A31
W
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Figure 9-4. Reset Boot Vector