Main Clock - Renesas M16C Series Hardware Manual

R8C/11 Group
The following describes the clocks generated by the clock generation circuit.

6.1 Main Clock

This clock is supplied by a main clock oscillation circuit. 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 X
IN
disconnected from the oscillator circuit during stop mode in order to reduce the amount of power con-
sumed in the chip. The main clock oscillator circuit may also be configured by feeding an externally
generated clock to the X
During reset and after reset, the main clock is turned off.
The main clock starts oscillating when the CM05 bit in the CM0 register is set to "0" (main clock on) after
setting the CM13 bit in the CM1 register to "1" (X
To use the main clock for the CPU clock, set the OCD2 bit in the OCD register to "0" (selecting main clock)
after the main clock becomes oscillating stably.
The power consumption can be reduced by setting the CM05 bit in the CM0 register to "1" (main clock off)
if the OCD2 bit is set to "1" (selecting on-chip oscillator clock).
Note that if an externally generated clock is fed into the X
setting the CM05 bit to "1". 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 Section 6.4, "Power Con-
trol."
Microcomputer
(Built-in feedback resistor)
X
I N
C
IN
N O T E S :
1 . I n s e r t a d a m p i n g r e s i s t o r i f r e q u i r e d . T h e r e s i s t a n c e w i l l v a r y d e p e n d i n g o n t h e o s c i l l a t o r a n d t h e o s c i l l a t i o n d r i v e
c a p a c i t y s e t t i n g . U s e t h e v a l u e r e c o m m e n d e d b y t h e m a k e r o f t h e o s c i l l a t o r .
W h e n t h e o s c i l l a t i o n d r i v e c a p a c i t y i s s e t t o l o w , c h e c k t h a t o s c i l l a t i o n i s s t a b l e . A l s o , i f t h e o s c i l l a t o r m a n u f a c t u r e r ' s
d a t a s h e e t s p e c i f i e s t h a t a f e e d b a c k r e s i s t o r b e a d d e d e x t e r n a l t o t h e c h i p , i n s e r t a f e e d b a c k r e s i s t o r b e t w e e n X
a n d X
O U T
Figure 6.5 Examples of Main Clock Connection Circuit
Rev.1.20 Jan 27, 2006
REJ09B0062-0120
and X pins. The main clock oscillator circuit contains a feedback resistor, which is
OUT
pin. Figure 6.5 shows examples of main clock connection circuit.
IN
X
O U T
(Note 1)
R
d
C
O U T
f o l l o w i n g t h e i n s t r u c t i o n .
page 34 of 204
- X pin).
IN OUT
pin, the main clock cannot be turned off by
IN
(Built-in feedback resistor)
X
I N
E x t e r n a l l y d e r i v e d c l o c k
Vcc
V s s
6.1 Main Clock
Microcomputer
X
OUT
O p e n
I N