Renesas rl78 User Manual
RL78/G1A
CHAPTER 5 CLOCK GENERATOR
R01UH0305EJ0200 Rev.2.00
139
Jul 04, 2013
CHAPTER 5 CLOCK GENERATOR
The presence or absence of connecting resonator pin for main system clock, connecting resonator pin for subsystem
clock, external clock input pin for main system clock, and external clock input pin for subsystem clock, depends on the
product.
Output pin
25, 32-pin
48, 64-pin
X1, X2 pins
√
√
EXCLK pin
√
√
XT1, XT2 pins
−
√
EXCLKS pin
−
√
5.1 Functions of Clock Generator
The clock generator generates the clock to be supplied to the CPU and peripheral hardware.
The following three kinds of system clocks and clock oscillators are selectable.
(1) Main system clock
<1> X1 oscillator
This circuit oscillates a clock of f
X
= 1 to 20 MHz by connecting a resonator to X1 and X2.
Oscillation can be stopped by executing the STOP instruction or setting of the MSTOP bit (bit 7 of the clock
operation status control register (CSC)).
<2> High-speed on-chip oscillator
The frequency at which to oscillate can be selected from among f
IH
= 32, 24, 16, 12, 8, 6, 4, 3, 2, or 1 MHz
(typ.) by using the option byte (000C2H). After a reset release, the CPU always starts operating with this
high-speed on-chip oscillator clock. Oscillation can be stopped by executing the STOP instruction or setting
the HIOSTOP bit (bit 0 of the CSC register).
The frequency specified by using an option byte can be changed by using the high-speed on-chip oscillator
frequency select register (HOCODIV). For details about the frequency, see Figure 5-9 Format of High-speed
On-chip Oscillator Frequency Select Register (HOCODIV).
The frequencies that can be specified for the high-speed on-chip oscillator by using the option byte and the
high-speed on-chip oscillator frequency select register (HOCODIV) are shown below.
Oscillation Frequency (MHz)
Power Supply Voltage
Flash Operation Mode
1 2 3 4 6 8 12
16
24
32
2.7 V
≤ V
DD
≤ 3.6 V
√
√
√
√
√
√
√
√
√
√
2.4 V
≤ V
DD
≤ 3.6 V
HS (high-speed main) mode
√
√
√
√
√
√
√
√
−
−
1.8 V
≤ V
DD
≤ 3.6 V
LS (low-speed main) mode
√
√
√
√
√
√
−
−
−
−
1.6 V
≤ V
DD
≤ 3.6 V
LV (low-voltage main) mode
√
√
√
√
−
−
−
−
−
−
An external main system clock (f
EX
= 1 to 20 MHz) can also be supplied from the EXCLK/X2/P122 pin. An external
main system clock input can be disabled by executing the STOP instruction or setting of the MSTOP bit.
As the main system clock, a high-speed system clock (X1 clock or external main system clock) or high-speed on-
chip oscillator clock can be selected by setting of the MCM0 bit (bit 4 of the system clock control register (CKC)).