NXP Semiconductors KE1xF Series, Reference Manual, Page: 624 / 1483

• 750 kHz
• 1 MHz
The current FlexCAN module can support up to 1 MHz speed. So the default speed is set
to 1 MHz.
In host applications, user can specify the speed for FlexCAN by giving the speed index 0
through 4 that represents those 5 speeds.
In Bootloader, it supports auto speed detection feature within supported speeds. The
Bootloader will enter the listen mode in the beginning with the initial speed (default
speed 1 MHz). Once the host starts sending a ping to a specific node, it will generate
traffic on FlexCAN bus. Since the Bootloader is in a listen mode, it will be able to check
if the local node speed is correct by detecting errors. If there is an error, that means we
see some traffic but may not be on the right speed to see the real data, it will change the
speed setting and check again. If there is no error, which means the speed should be
correct, now it changes the settings back to normal receiving mode to see if there is a
package for this node. (It then will stay in this speed until another host is using another
speed and try to communicate with any node. It will repeat the process to detect a right
speed before sending host timeout and abort the request.)
The host side should also have reasonable time tolerance during the auto speed detect
period. If the sending is timeout, which means there is no response from the specific node
or there is a real error, it will need to report the error to the application.
The following flow charts demonstrate the communication flow of how the host reads
ping packet, ACK and response from the target.
Figure 23-25. Host reads ping response from target via FlexCAN
Peripherals Supported
Kinetis KE1xF Sub-Family Reference Manual, Rev. 4, 06/2019
624 NXP Semiconductors