
MB91360G Series
152
28. SUBCLOCK
The Subclock System provides various power saving modes. The key of the concept is to supply the 32 kHz
clock signal only to the Real Time Clock RTC) Module, while the rest of the MCU is provided with 4 MHz clock
signal in order to achieve lower power supply current in the RTC32K mode.
This behavior can be altered by the configuration input, SELCLK pin to switch the RTC module to operate with
the 4 MHz clock. The following sections describe the operation with SELCLK connected to “0” and SELCLK
connected to “1” respectively.
Note : On MB91F361GA and MB91F362GA SELCLK should always be connected to “1”, subclock operation is not
implemented on those devices.
(1) Operation of Subclock (SELCLK
=
0)
The next table summarizes the operation states of the components related to the Subclock System.To simplify
this table SLEEP modes are not listed but the operation is the same as for RUN modes except that the CPU is
stopped.
The following table summarizes those operation modes and necessary software settings.
It is recommended that PLL2EN is set to “1” after the initialization to start the 32 kHz oscillation and this bit
should be kept at “1” during the operation. Otherwise the 32 kHz oscillator does not start. Also bits 9 and 10 of
the CLKR register (address 0046H) should always be set to “0” during operation.
Mode
Power dissipation
Operation of components
4 M Osc.
32 K Osc.
RTC
CPU &
Peripheral
PLL
RUN
High
Run
Run
Run
Run
Stop/Run
RTC4M32K
Medium Low
Run
Run
Run
Stop
Stop
RTC32K
Low
Stop
Run
Run
Stop
Stop
STOP
Lowest
Stop
Stop
Stop
Stop
Stop
Mode
Software Setting
STOP
PLL1EN
PLL2EN
OSCD1
OSCD2
RTC32
RUN
0
0 or 1
1
Don’t Care
Don’t Care
Don’t Care
RTC4M32K
1
Don’t Care
1
0
0
Don’t Care
RTC32K
1
Don’t Care
1
1
0
1
STOP
1
Don’t Care
Don’t Care
1
1
Don’t Care