EM78156EAS EMC [ELAN Microelectronics Corp], EM78156EAS Datasheet - Page 27

• Manufacturer Part Number: EM78156EAS
• Description: 8-Bit Microcontroller with MASK ROM
• Manufacturer: EMC [ELAN Microelectronics Corp]

Product Specification (V1.3) 07.29.2004
(This specification is subject to change without further notice)
In the most applications, Pin OSCI and Pin OSCO can be connected with a crystal or
ceramic resonator to generate oscillation. Fig. 12 depicts such circuit. The same thing
applies whether it is in the HXT mode or in the LXT mode. Table 10 provides the
recommended values of C1 and C2. Since each resonator has its own attribute, user
should refer to its specification for appropriate values of C1 and C2. RS, a serial
resistor, may be necessary for AT strip cut crystal or low frequency mode.
Table 10 Capacitor Selection Guide for Crystal Oscillator or Ceramic Resonator
4.7.3 External RC Oscillator Mode
For some applications that do not need a very precise timing calculation, the RC
oscillator (Fig. 15) offers a lot of cost savings. 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 the
manufacturing process variation.
In order to maintain a stable system frequency, the values of the Cext should not be
less than 20pF, and that the value of Rext should not be greater than 1 M ohm. If they
cannot be kept in this range, the frequency is easily affected by noise, humidity, and
leakage.
Ceramic Resonators
Crystal Oscillator
Oscillator Type
EM78156E
Fig. 12 Circuit for Crystal/Resonator
OSCO
OSCI
Frequency Mode
XTAL
RS
HXT
HXT
LXT
C1
C2
8-Bit Microcontroller with MASK ROM
Frequency
32.768kHz
455 kHz
2.0 MHz
4.0 MHz
100KHz
200KHz
455KHz
1.0MHz
2.0MHz
4.0MHz
100~150
C1(pF)
20~40
10~30
20~40
15~30
25
25
25
15
15
EM78156E
100~150
20~150
C2(pF)
20~40
10~30
15~30
15
25
25
15
15
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