NXP Semiconductors K32 L2A Series, Reference Manual, Page: 307 / 1379

14.4.4 LPUART Peripheral
The Kinetis Bootloader integrates an autobaud detection algorithm for the LPUART
peripheral, thereby providing flexible baud rate choices.
Autobaud feature: If LPUARTn is used to connect to the bootloader, then the
LPUARTn_RX pin must be kept high and not left floating during the detection phase in
order to comply with the autobaud detection algorithm. After the bootloader detects the
ping packet (0x5A 0xA6) on LPUARTn_RX, the bootloader firmware executes the
autobaud sequence. If the baudrate is successfully detected, then the bootloader will send
a ping packet response [(0x5A 0xA7), protocol version (4 bytes), protocol version
options (2 bytes) and crc16 (2 bytes)] at the detected baudrate. The Kinetis Bootloader
then enters a loop, waiting for bootloader commands via the LPUART peripheral.
NOTE
• The autobaud feature requires a ping packet with a higher
accuracy (+/-3%), or the ping packet will be ignored as
noise.
• The data bytes of the ping packet must be sent continuously
(with no more than 80 ms between bytes) in a fixed
LPUART transmission mode (8-bit data, no parity bit and 1
stop bit). If the bytes of the ping packet are sent one-by-one
with more than 80 ms delay between them, then the
autobaud detection algorithm may calculate an incorrect
baud rate. In this case, the autobaud detection state machine
should be reset.
Supported baud rates: The baud rate is closely related to the MCU core and system
clock frequencies. Typical baud rates supported are 9600, 19200, 38400, 57600, and
115200. Of course, to influence the performance of autobaud detection, the clock
configuration in BCA can be changed.
Packet transfer: After autobaud detection succeeds, bootloader communications can
take place over the LPUART peripheral. The following flow charts show:
• How the host detects an ACK from the target
• How the host detects a ping response from the target
• How the host detects a command response from the target
Chapter 14 Kinetis ROM Bootloader
K32 L2A Reference Manual, Rev. 2, 01/2020
NXP Semiconductors 307