UPD78F0838 Renesas Electronics Corporation., UPD78F0838 Datasheet - Page 630

• Manufacturer Part Number: UPD78F0838
• Description: 8-bit Single-chip Microcontrollers
• Manufacturer: Renesas Electronics Corporation.

15.14 Time Stamp Function
a consequence, the clocks of the nodes have no relation (i.e., the clocks are asynchronous and may have different
frequencies).
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.
15.14.1 Time stamp function
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. TSOUT signal can be selected from the
following two event sources and is specified by the TSSEL bit of the C0TS register.
timing diagram, the SOF is used as the trigger event source). To capture a timer value by using TSOUT signal, the
capture timer unit must detect the capture signal at both the rising edge and falling edge.
TSOUT bit toggles upon occurrence of the selected event. If TSLOCK bit is set to 1, TSOUT toggles upon occurrence
of the selected event, but the toggle is stopped as the TSEN bit is automatically cleared to 0 as soon as the message
storing to the message buffer 0 starts. This suppresses the subsequent toggle occurrence by TSOUT, 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.
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CAN is an asynchronous, serial protocol. All nodes connected to the CAN bus have a local, autonomous clock. As
In some applications, however, a common time base over the network (= global time base) is needed. In order to
The CAN controller supports the capturing of timer values triggered by a specific frame. An on-chip 16-bit capture
- SOF event (start of frame)
- EOF event (last bit of end of frame) (TSSEL = 1)
The TSOUT signal is enabled by setting the TSEN bit of the C0TS register to 1.
TSOUT signal toggles its level upon occurrence of the selected event during data frame reception (in the above
This time stamp function is controlled by the TSLOCK bit of the C0TS register. When TSLOCK is cleared to 0,
TSOUT
SOF
Figure 15-35. Timing Diagram of Capture Signal TSOUT
(TSSEL = 0)
Preliminary User’s Manual U19748EJ1V0UD
CHAPTER 15 CAN CONTROLLER
SOF
SOF
SOF
t