Datasheet

V850ES/JG3-H, V850ES/JH3-H CHAPTER 20 CAN CONTROLLER
R01UH0042EJ0500 Rev.5.00 Page 1007 of 1513
Aug 12, 2011
20.14 Time Stamp Function
CAN is an asynchronous, serial protocol. All nodes connected to the CAN bus have a local, autonomous clock. As a
consequence, the clocks of the nodes have no relation (i.e., the clocks are asynchronous and may even have different
frequencies).
In some applications, however, a common time base over the network (= global time base) is needed. In order to build
up a global time base, a time stamp function is used. The essential mechanism of a time stamp function is the capture of
timer values triggered by signals on the CAN bus.
20.14.1 Time stamp function
The CAN controller supports the capturing of timer values triggered by a specific frame. An on-chip 16-bit capture timer
unit in a microcontroller system is used in addition to the CAN controller. The 16-bit capture timer unit captures the timer
value according to a trigger signal (TSOUT) for capturing that is output when a data frame is received from the CAN
controller. The CPU can retrieve the time of occurrence of the capture event, i.e., the time stamp of the message received
from the CAN bus, by reading the captured value. The TSOUT signal can be selected from the following two event
sources and is specified by the C0TS.TSSEL bit.
• SOF event (start of frame) (TSSEL bit = 0)
• EOF event (last bit of end of frame) (TSSEL bit = 1)
The TSOUT signal is enabled by setting the C0TS.TSEN bit to 1.
Figure 20-35. Timing Diagram of Capture Signal TSOUT
t
TSOUT
SOF
SOF
SOF
SOF
The TSOUT signal toggles its level upon occurrence of the selected event during data frame reception (in Figure 20-34,
the SOF is used as the trigger event source). To capture a timer value by using the TSOUT signal, the capture timer unit
must detect the capture signal at both the rising edge and falling edge.
This time stamp function is controlled by the C0TS.TSLOCK bit. When the TSLOCK bit is cleared to 0, the TSOUT
signal toggles upon occurrence of the selected event. If the TSLOCK bit is set to 1, the TSOUT signal toggles upon
occurrence of the selected event, but the toggle is stopped as the TSEN bit is automatically cleared to 0 when a data
frame starts to be received and stored in message buffer 0. This suppresses the subsequent toggle occurrence by the
TSOUT signal, so that the time stamp value toggled last (= captured last) can be saved as the time stamp value of the
time at which the data frame was received in message buffer 0.