User guide

SmartBook for Renesas R8C/Tiny Microcontrollers

www.MightyMicons.com

Chapter 2. Clock Generating Mechanism

2.1 Introduction:

R8C/Tiny microcontrollers sport a versatile clock generating mechanism to protect

the controller’s operations against going awry on the account of system clock

becoming faulty at any time. For this purpose, the device comes with built-in

Ring Oscillators to supply the required clock source to the CPU and the peripherals,

in case the main clock derived from the externally connected crystal or the

resonator becomes defective. As the result, the system’s reliability is very much

improved.

The controller’s clock generating circuit gets two clock sources: A main clock

source using external crystal or resonator and the internal ring oscillator circuit.

The main clock operates up to 20MHz using the external crystal. The internal

Ring oscillator operates independent of main clock and generates two clock signals

on its own. Low speed Ring Oscillator with about 125KHz and the high speed

Ring oscillator capable of generating the nominal clock signal of 8MHz with the

facility to vary the same from 5 MHz to 16 MHz. There is a control register

associated with the high speed ring oscillator to define the exact frequency of the

clock with the accuracy of +/- 1 nano seconds.

The Micon’s clock generating circuit also contains an Oscillator Stop Detection

function to monitor the main clock source. When the main clock source fails or

disconnected from the device, the oscillator stop detecting function automatically

substitutes the clock source of low speed ring oscillator to the CPU and the

peripheral functions to maintain the CPU operation or enables

the orderly shut down.

The same oscillation detect function works in

association with built-in voltage detection

circuit to feed the CPU and the peripherals

with the low speed ring oscillator till the

main clock gets stabilized during power

on or reset release conditions. Once the

main clock becomes stable, the

application can switch from low speed

The

device comes with

built-in Ring Oscillators to

supply the required clock source

to the CPU and the peripherals, in

case the main

clock derived

from the externally

connected crystal or

the resonator becomes

defective.