Example Of Using Power Saving Modes - NEC V850E/RS1 User Manual

16.11.3 Example of using power saving modes

In some application systems, it may be necessary to place the CPU in a power saving mode to reduce
the power consumption. By using the power saving mode specific to the CAN module and the power
saving mode specific to the CPU in combination, the CPU can be woken up from the power saving sta-
tus by the CAN bus.
Here is an example of using the power saving modes.
First, put the CAN module in the CAN sleep mode (PSMODE = 01B). Next, put the CPU in the power
saving mode. If an edge transition from recessive to dominant is detected at the CAN reception pin
(CRXDn) in this status, the CINTS5 bit in the CAN module is set to 1. If the CIE5 bit of the CnCTRL reg-
ister is set to 1, a wake-up interrupt (INTWUP) is generated. The CAN module is automatically released
from the CAN sleep mode (PSMODE = 00B) and returns to the normal operation mode. The CPU, in
response to INTWUP, can release its own power saving mode and return to the normal operation mode.
To further reduce the power consumption of the CPU, the internal clocks, including that of the CAN
module, may be stopped. In this case, the operating clock supplied to the CAN module is stopped after
the CAN module is put in the CAN sleep mode. Then the CPU enters a power saving mode in which the
clock supplied to the CPU is stopped. If an edge transition from recessive to dominant is detected at the
CAN reception pin (CRXDn) in this status, the CAN module can set the CINTS5 bit to 1 and generate
the wake-up interrupt (INTWUP) even if it is not supplied with the clock. The other functions, however,
do not operate because clock supply to the CAN module is stopped, and the module remains in the
CAN sleep mode. The CPU, in response to INTWUP, releases its power saving mode, resumes supply
of the internal clocks, including the clock to the CAN module, after the oscillation stabilization time has
elapsed, and starts instruction execution. The CAN module is immediately released from the CAN
sleep mode when clock supply is resumed, and returns to the normal operation mode
(PSMODE = 00B).
Remark:
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Chapter 16 FCAN Controller
n = 0, 1
m = 0 to 31
User's Manual U16702EE3V2UD00