R8C/36T-A Group
9. Clock Generation Circuit
Under development Preliminary document
Specifications in this document are tentative and subject to change.
R01UH0240EJ0010 Rev.0.10
Page 95 of 728
Aug 05, 2011
9.3
XIN Clock
The XIN clock is supplied by the XIN clock oscillation circuit. This clock is used as the clock source for the CPU
clock and the peripheral function clock. The XIN clock oscillation circuit is configured by connecting an oscillator
between pins XIN and XOUT. The XIN clock oscillation circuit includes an on-chip feedback resistor, which is
disconnected from the oscillation circuit in stop mode to reduce power consumption. The XIN clock oscillation
circuit also allows an externally generated clock to be input to the XOUT pin.
The XIN clock is stopped during and after a reset.
After setting the CM13 bit in the CM1 register to 1 (XIN-XOUT pin), when the CM05 bit in the CM0 register is set
to 0 (XIN clock oscillates), the XIN clock starts oscillating. After the XIN clock oscillation stabilizes, when bits
CM42 to CM40 in the CM4 register are set to 000b (XIN clock selected), the XIN clock is used as the clock source
for the CPU.
In stop mode, all clocks including the XIN clock are stopped. For details, refer to 10. Power Control.
The settings listed in
Table 9.5 are necessary to set the XIN clock, corresponding to the external oscillator or
external clock input.
Figure 9.3
Connection Examples of XIN Clock Oscillation Circuit
Table 9.5
CM0 and CM1 Register Settings
CM0 Register
CM1 Register
XIN Clock
CM05 Bit
CM07 Bit
CM13 Bit
1
0
1
Oscillation stops
0
1
Oscillation enabled
1
External clock stops
0
1
External clock input enabled
XIN
XOUT
MCU
(on-chip feedback resistor)
Rd
(1)
COUT
CIN
XIN
XOUT
MCU
(on-chip feedback resistor)
Externally generated clock
VCC
VSS
Open
External ceramic resonator connected circuit
External clock input circuit
Rf
(1)
When CM05 bit in CM0 register is 0
(oscillates), CM07 bit in CM0 register
to 0 (XIN clock is supplied by oscillator
(external ceramic resonator, etc.)),
and CM13 bit in CM1 register is 1
(XIN-XOUT pin)
When CM05 bit in CM0 register is 0
(oscillates), CM07 bit in CM0 register
to 1 (XIN clock is supplied by external
clock input to XOUT pin), and CM13
bit in CM1 register is 1 (XIN-XOUT
pin)
(2)
Notes:
1. Insert a damping resistor if necessary. The resistance will vary depending on the oscillator and the
oscillation drive capacity. Use the values recommended by the oscillator manufacturer.
If the manufacturer specifies that a feedback resistor be added to the chip externally, insert a feedback
resistor between XIN and XOUT following the instructions.
2. Insert a damping resistor if required to prevent overshoot from occurring.