M306H7MG-XXXFP Datasheet, PDF (30/329 Pages) Renesas Technology Corp – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER with DATA ACQUISITION CONTROLLER

M306H7MG-XXXFP/MC-XXXFP/FGFP
4. CLOCK GENERATION CIRCUIT
4.1 Oscillator Circuit
The following describes the clocks generated by the clock generation circuit.
Two oscillation circuits are built in the clock generating circuit, and a main clock or a sub clock can be chosen as a
CPU clock by setup of the STARTB pin after reset.
4.1.1 Main Clock
This clock is used as the clock source for the CPU and peripheral function clocks. The main clock oscillator
circuit is configured by connecting a resonator between the XIN and XOUT pins. The main clock oscillator
circuit contains a feedback resistor, which is disconnected from the oscillator circuit during stop mode in order
to reduce the amount of power consumed in the chip. The main clock oscillator circuit may also be configured
by feeding an externally generated clock to the XIN pin. Figure 4.5 shows the examples of main clock
connection circuit.
When the level on the STARTB pin is “L”, the main clock divided by 8 is selected for the CPU clock (Sub
clock turned off) after reset.
The power consumption in the chip can be reduced by setting the CM05 bit of CM0 register to “1” (main clock
oscillator circuit turned off) after switching the clock source for the CPU clock to a sub clock. In this case,
XOUT goes “H”. Furthermore, because the internal feedback resistor remains on, XIN is pulled “H” to XOUT via
the feedback resistor. Note that if an externally generated clock is fed into the XIN pin, the main clock cannot be
turned off by setting the CM05 bit to “1” without selecting sub clock for the CPU clock. If necessary, use an
external circuit to turn off the clock.
During stop mode, all clocks including the main clock are turned off. Refer to “power control”.
Microcomputer
(Built-in feedback resistor)
XIN
XOUT
(Note)
Rd
CIN
COUT
Microcomputer
(Built-in feedback resistor)
XIN
XOUT
Open
Externally derived clock
Vcc
Vss
Note: Insert a damping resistor if required. The resistance will vary depending on the oscillator and the oscillation drive
capacity setting. Use the value recommended by the maker of the oscillator.
When the oscillation drive capacity is set to low, check that oscillation is stable. Also, if the oscillator manufacturer's
data sheet specifies that a feedback resistor be added external to the chip, insert a feedback resistor between XIN
and XOUT following the instruction.
Figure 4.5 Examples of Main Clock Connection Circuit
Rev.2.10 Oct 25, 2006 Page 30 of 326
REJ03B0152-0210