EM78P458/459
OTP ROM
below.
Ext.
OSCI
Clock
EM78P458
EM78P459
OSCO
Fig. 18 Circuit for External Clock Input
In the most applications, pin OSCI and pin OSCO can be connected with a crystal or ceramic
resonator to generate oscillation. Fig. 19 depicts such circuit. The same applies to the HXT mode and
the LXT mode. Table 12 provided the recommended values of C1 and C2. Since each resonator has
its own attribute, user should refer to their specifications for appropriate values of C1 and C2. RS, a
serial resistor, may be necessary for AT strip cut crystal or low frequency mode.
C1
OSCI
EM78P458
EM78P459
XTAL
RS
OSCO
C2
Fig. 19 Circuit for Crystal/Resonator
Table 13 Capacitor Selection Guide for Crystal Oscillator or Ceramic Resonators
Oscillator Type
Frequency Mode
Frequency
C1(pF)
C2(pF)
455 kHz
2.0 MHz
4.0 MHz
32.768kHz
100KHz
200KHz
455KHz
1.0MHz
2.0MHz
4.0MHz
100~150
20~40
10~30
25
100~150
20~40
10~30
15
Ceramic
HXT
Resonators
LXT
HXT
25
25
25
25
Crystal Oscillator
20~40
15~30
15
20~150
15~30
15
15
15
3. External RC Oscillator Mode
For some applications that do not require precise timing calculation, the RC oscillator (Fig. 20) could
This specification is subject to change without prior notice.
46
06.25.2004 (V1.4)
ELAN [ ELAN MICROELECTRONICS CORP ]
