NXP Semiconductors KE1xF Series, Reference Manual, Page: 1455 / 1483

50.5.8.3 Time stamp
The value of the Free Running Timer is sampled at the beginning of the Identifier field on
the CAN bus, and is stored at the end of "move-in" in the TIME STAMP field, providing
network behavior with respect to time.
When the TIMER_SRC bit in CAN_CTRL2 register is asserted, the Free Running Timer
is continuously clocked by an external time tick.
When the TIMER_SRC bit in CAN_CTRL2 register is negated, the Free Running Timer
is clocked by the FlexCAN bit-clock, which defines the baud rate on the CAN bus.
During a message transmission/reception, it increments by one for each bit that is
received or transmitted. When there is no message on the bus, it counts using the
previously programmed baud rate.
The Free Running Timer is not incremented during Disable, Stop, and Freeze modes. It
can be reset upon a specific frame reception, enabling network time synchronization. See
the TSYN description in Control 1 Register (CAN_CTRL1).
50.5.8.4 Protocol timing
The following figure shows the structure of the clock generation circuitry that feeds the
CAN Protocol Engine (PE) submodule. The clock source bit CLKSRC in the
CAN_CTRL1 Register defines whether the internal clock is connected to the output of a
crystal oscillator (Oscillator Clock) or to the Peripheral Clock. In order to guarantee
reliable operation, the clock source should be selected while the module is in Disable
Mode (MDIS bit set in the Module Configuration Register).
NOTE
Please refer to the clock distribution chapter (module clocks
table) to identify the proper clock source.
CAN_CTRL1[CLKSRC]
Sclock CANCLK
Prescaler
Peripheral Clock
Oscillator Clock
(Tq)
1
0
Figure 50-2. CAN engine clocking scheme
Chapter 50 CAN (FlexCAN)
Kinetis KE1xF Sub-Family Reference Manual, Rev. 4, 06/2019
NXP Semiconductors 1455