EM78P417N/418N/419N
8-Bit Microprocessor with OTP ROM
In order to maintain a stable system frequency, the values of the Cext should be no less
than 20pF, and that the value of Rext should be no greater than 1MΩ. If the frequency
cannot be kept within this range, the frequency can be affected easily by noise,
humidity, and leakage.
The smaller the Rext in the RC oscillator is, 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 supply voltage, the
operation temperature, the components of the RC oscillator, the package types, and
the way the PCB is layout, have certain effect on the system frequency.
The RC Oscillator frequencies:
Cext
Rext
Average Fosc 5V,25°C
Average Fosc 3V,25°C
3.3k
5.1k
10k
3.5 MHz
2.5 MHz
1.30 MHz
140 KHz
1.27 MHz
850 KHz
450 KHz
48 KHz
3.2 MHz
2.3 MHz
1.25 MHz
140 KHz
1.21 MHz
820 KHz
450 KHz
50 KHz
20 pF
100k
3.3k
5.1k
10k
100 pF
300 pF
100k
3.3k
5.1k
10k
560 KHz
370 KHz
196 KHz
20 KHz
540 KHz
360 KHz
192 KHz
20 KHz
100k
NOTE: 1. Measured on DIP packages.
2. Design reference only
3. The frequency drift is about ±30%
6.11.4 Internal RC Oscillator Mode
EM78P417/8/9N offers a versatile internal RC mode with default frequency value of
4MHz. Internal RC oscillator mode has other frequencies (1MHz, 8MHz, and 455KHz)
that can be set by CODE OPTION (WORD1), RCM1, and RCM0. Table below
describes the EM78P417/8/9N internal RC drift with the variation of voltage,
temperature, and process.
Product Specification (V1.0) 06.23.2005
• 59
(This specification is subject to change without further notice)
ELAN [ ELAN MICROELECTRONICS CORP ]
