em78p210n ELAN Microelectronics Corp, em78p210n Datasheet - Page 50

• Manufacturer Part Number: em78p210n
• Description: 8-bit Microcontroller With Otp Rom
• Manufacturer: ELAN Microelectronics Corp

EM78P210N
8-Bit Microcontroller with OTP ROM
44 •
6.8.3
For some applications that do not require
precise timing calculation, the RC
oscillator (Figure 6-16) could offer a cost-
effective oscillator configuration.
Nevertheless, it should be noted that the
frequency of the RC oscillator is
influenced by the supply voltage, the
values of the resistor (Rext), the capacitor
(Cext), and even by the operation
temperature. Moreover, the frequency
also changes slightly from one chip to
another due to manufacturing process
variations.
In order to maintain a stable system frequency, the values of the Cext should not be
less than 20pF, and the value of Rext should not be greater than 1MΩ. If the frequency
cannot be kept within this range, the frequency can be easily affected by noise,
humidity, and leakage.
The smaller the Rext in the RC oscillator, the faster its frequency will be. On the
contrary, for very low Rext values, for instance, 1 KΩ, the oscillator will become
unstable because the NMOS cannot discharge the capacitance current correctly.
Based on the above reasons, it must be kept in mind that all the supply voltage, the
operation temperature, the components of the RC oscillator, the package types, and
the PCB is layout, have certain effect on the system frequency.
The RC Oscillator frequencies:
Note:
100 pF
300 pF
20 pF
Cext
2
3
1
:
:
:
The values are for design reference only.
The frequency drift is ± 30%
Measured based on DIP packages.
External RC Oscillator Mode
Rext
100k
100k
100k
3.3k
5.1k
3.3k
5.1k
3.3k
5.1k
10k
10k
10k
Average Fosc 5V, 25 ° C
(This specification is subject to change without further notice)
1.30 MHz
1.27 MHz
3.5 MHz
2.5 MHz
140kHz
850kHz
450kHz
560kHz
370kHz
196kHz
48kHz
20kHz
Figure 6-16 External RC Oscillator Mode
Product Specification (V1.2) 04.22.2008
OSCI
Average Fosc 3V, 25 ° C
Circuit
1.25 MHz
1.21 MHz
3.2 MHz
2.3 MHz
140kHz
820kHz
450kHz
540kHz
360kHz
192kHz
50kHz
20kHz
Vcc
Rext
Cext