Chapter 5 Clock Generator; Functions Of Clock Generator - Renesas RL78/G1P Hardware User Manual

RL78/G1P

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
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
(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).
An external main system clock (f
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)).
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
highspeed on-chip oscillator frequency select register (HOCODIV) are shown below.
Power Supply Voltage
2.7 V ≤ V ≤ 3.6 V
DD
Note that the usable frequency range of the main system clock differs depending on the setting of the power supply
voltage (V ). The operating voltage of the flash memory must be set by using the CMODE0 and CMODE1 bits of
DD
the option byte (000C2H) (see CHAPTER 22 OPTION BYTE).
(2) Low-speed on-chip oscillator clock (Low-speed On-chip oscillator)
This circuit oscillates a clock of f
The low-speed on-chip oscillator clock cannot be used as the CPU clock.
Only the following peripheral hardware runs on the low-speed on-chip oscillator clock.
 Watchdog timer
This clock operates when bit 4 (WDTON) of the option byte (000C0H) is set to 1.
However, when WDTON = 1and bit 0 (WDSTBYON) of the option byte (000C0H) is 0, oscillation of the low-
speed on-chip oscillator stops if the HALT or STOP instruction is executed.
Remark f : X1 clock oscillation frequency
X
f : High-speed on-chip oscillator clock frequency
IH
f : External main system clock frequency
EX
f : Low-speed on-chip oscillator clock frequency
IL
R01UH0895EJ0100 Rev.1.00
Nov 29, 2019

CHAPTER 5 CLOCK GENERATOR

= 1 to 20 MHz by connecting a resonator to X1 and X2.
X
= 1 to 20 MHz) can also be supplied from the EXCLK/X2/P122 pin. An external
EX
Oscillation Frequency (MHz)
1 2 3
  
= 15 kHz (TYP.).
IL
CHAPTER 5 CLOCK GENERATOR
= 32, 24, 16, 12, 8, 6, 4, 3, 2, or 1 MHz
IH
4 6 8 12
  
16 24 32
   
96