7540 Group User’s Manual
APPLICATION
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2.9 Oscillation control
2.9.6 Notes on oscillation stop detection circuit
Notes on using oscillation stop detection circuit are described below.
(1) Note on ring oscillator
The 7540 Group starts operation by the ring oscillator.
(2) Notes on oscillation circuit stop detection circuit
When the stop mode is used, set the oscillation stop detection function to “invalid”.
When f(XIN) oscillation is stopped, set the oscillation stop detection function to “invalid”.
The oscillation stop detection circuit is not included in the emulator MCU “M37540RSS”.
(3) Notes on stop mode
When the stop mode is used, set the oscillation stop detection function to “invalid”.
When the stop mode is used, set “0” (STP instruction enabled) to the STP instruction disable bit
of the watchdog timer control register.
Timer 1 can be used to set the oscillation stabilizing time after release of the STP instruction. The
oscillation stabilizing time after release of STP instruction can be selected from “set automatically”/
“not set automatically” by the oscillation stabilizing time set bit after release of the STP instruction
of MISRG. When “0” is set to this bit, “0116” is set to timer 1 and “FF16” is set to prescaler 1
automatically. When “1” is set to this bit, nothing is set to timer 1 and prescaler 1. Therefore, set
the wait time according to the oscillation stabilizing time of the oscillation. Also, when timer 1 is
used, set values again to timer 1 and prescaler 1 after system is returned from the stop mode.
The STP instruction cannot be used during CPU is operating by the ring oscillator.
When the stop mode is used, stop the ring oscillator oscillation.
Do not execute the STP instruction during the A-D conversion.
(4) Note on wait mode
When the wait mode is used, stop the clock except the operation clock source.
(5) Notes on state transition
When the operation clock source is f(XIN), the CPU clock division ratio can be selected from the
following;
f(XIN)/2 (high-speed mode)
f(XIN)/8 (middle-speed mode)
f(XIN) (double-speed mode)
The double-speed mode can be used only at ceramic oscillation.
Do not use the mode at RC oscillation.
Stabilize the f(XIN) oscillation to change the operation clock source from the ring oscillator to f(XIN).