EM78156E Datasheet, PDF (28/48 Pages) ELAN Microelectronics Corp – 8-Bit Microcontroller with MASK ROM

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
EM78156E
Cext
Fig. 13 Circuit for External RC Oscillator Mode
Table 11 RC Oscillator Frequencies
Cext
20 pF
100 pF
300 pF
Rext
3.3k
5.1k
10k
100k
3.3k
5.1k
10k
100k
3.3k
5.1k
10k
100k
Average Fosc
5V,25°C
3.92 MHz
2.67 MHz
1.39 MHz
149 KHz
1.39 MHz
940 KHz
480 KHz
52 KHz
595 KHz
400 KHz
200 KHz
21 KHz
Average Fosc
3V,25°C
3.65 MHz
2.60 MHz
1.40 MHz
156 KHz
1.33 MHz
920 KHz
475 KHz
50 KHz
560 KHz
390 KHz
200 KHz
20 KHz
NOTE
1. Measured on DIP packages.
2. For design reference only.
3. The frequency drift is about Ô30%
24 •
Product Specification (V1.3) 07.29.2004
(This specification is subject to change without further notice)