RL78/D1A User's Manual: Hardware - Renesas

Under development
Preliminary document
Specifications in this document are tentative and subject to change.
RL78/D1A CHAPTER 14 CAN CONTROLLER
14.14 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 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.
14.14.1 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. TSOUT signal can be selected from the following two event sources
and is specified by the TSSEL bit of the C0TS register.
- SOF event (start of frame) (TSSEL = 0)
- 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
Figure 14-61. Timing Diagram of Capture Signal TSOUT
SOF SOF SOF SOF
TSOUT signal toggles its level upon occurrence of the selected event during data frame reception (in the above 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.
This time stamp function is controlled by the TSLOCK bit of the C0TS register. When TSLOCK is cleared to 0, 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.
R01UH0317EJ0004 Rev. 0.04 909
Feb. 22, 2013
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