SIM225 Technical Reference Manual
42
© Serious Integrated, Inc.
SIM225_TRM_A1ENUS
Revision A1
2)
The relatively accurate 12MHz clock to the MCU, which is multiplied and divided in a variety of
ways inside the MCU to generate the 96MHz the MCU runs at as well as all the different peripheral
clocks.
CPU AND PERIPHERAL CLOCKS
The SIM225 uses the external 12MHz oscillator module attached to the MCU’s input clock circuit as the
primary source for all non-timekeeping clocks in the system.
The RX MCU, like all modern MCUs, has sophisticated internal clock management circuitry which takes a
few input clock frequencies and delivers a plethora of derivative clocks; some higher frequency, some
lower. For instance, the RX MCU can take a single 12MHz input clock and create derivative clocks such as
the core 96MHz CPU clock as well as various peripheral clocks including 48MHz required for the 12mbps
USB ports, 9600 baud for a UART serial port, 48MHz for the SRAM bus, etc. While the RX63x MCU family
used on the SIM225 can operate up to 100MHz, on the SIM225 it should typically be programmed to
operate at 96MHz so that all the other peripherals can divide down properly from that top frequency. The
complexity and capabilities of the RX family clock system are beyond the scope of this guide: consult the
Renesas documentation for a complete description.
MCU ON-CHIP BATTERY BACKED REAL-TIME CLOCK/CALENDAR
Time keeping (i.e. year/month/day/hour/etc.) can be performed using the RX MCU’s internal Real Time
Clock/Calendar peripheral if the family member has the 32.768 KHz crystal populated on the module.
The RTCC peripheral must be configured (via software and registers) to be enabled and use that clock
input correctly.
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