M306H7MG-XXXFP Datasheet, PDF (31/329 Pages) Renesas Technology Corp – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER with DATA ACQUISITION CONTROLLER

M306H7MG-XXXFP/MC-XXXFP/FGFP
4. CLOCK GENERATION CIRCUIT
4.1.2 Sub Clock
The sub clock is generated by the sub clock oscillation circuit. This clock is used as the clock source for the
CPU clock, as well as the timer A and timer B count sources. In addition, an fc clock with the same frequency
as that of the sub clock can be output from the CLKOUT pin.
The sub clock oscillator circuit is configured by connecting a crystal resonator between the XCIN and XCOUT
pins. The sub 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 sub clock oscillator
circuit may also be configured by feeding an externally generated clock to the XCIN pin.
Figure 4.6 shows the examples of sub clock connection circuit.
When the level on the STARTB pin is “L ”, the sub clock is turned off after reset. At this time, the feedback
resistor is disconnected from the oscillator circuit.
To use the sub clock for the CPU clock, set the CM07 bit of CM0 register to “1 ” (sub clock) after the sub clock
becomes oscillating stably.
When a STARTB pin is “H ”, the sub clock (XCIN) divided by 8 becomes the CPU clock after reset (the main
clock stops). When you use a main clock after this, please shift according to the procedure shown in Fig. 4.7.
During stop mode, all clocks including the sub clock are turned off. Refer to “power control”.
Microcomputer
(Built-in feedback resistor)
XCIN
XCOUT
(Note)
RCd
CCIN
CCOUT
Microcomputer
(Built-in feedback resistor)
XCIN
XCOUT
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 XCIN
and XCOUT following the instruction.
Figure 4.6 Examples of Sub Clock Connection Circuit
Rev.2.10 Oct 25, 2006 Page 31 of 326
REJ03B0152-0210