EM78156E
8-Bit Microcontroller with MASK ROM
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 becomes unstable
because the NMOS cannot discharge the current of the capacitance correctly.
Based on the above reasons, it must be kept in mind that all of the supply voltage, the
operation temperature, the components of the RC oscillator, the package types, the
way the PCB is layout, will affect the system frequency.
Vcc
Rext
OSCI
Cext
EM78156E
Fig. 13 Circuit for External RC Oscillator Mode
Table 11 RC Oscillator Frequencies
Average Fosc
Average Fosc
Cext
Rext
5V,25°C
3V,25°C
3.3k
5.1k
10k
3.92 MHz
2.67 MHz
1.39 MHz
149 KHz
1.39 MHz
940 KHz
480 KHz
52 KHz
3.65 MHz
2.60 MHz
1.40 MHz
156 KHz
1.33 MHz
920 KHz
475 KHz
50 KHz
20 pF
100k
3.3k
5.1k
10k
100 pF
300 pF
100k
3.3k
5.1k
10k
595 KHz
400 KHz
200 KHz
21 KHz
560 KHz
390 KHz
200 KHz
20 KHz
100k
NOTE
1. Measured on DIP packages.
2. For design reference only.
3. The frequency drift is about ±30%
24 •
Product Specification (V1.3) 07.29.2004
(This specification is subject to change without further notice)
ELAN [ ELAN MICROELECTRONICS CORP ]
