ELAN Home Systems EM78P458 - Manual (Page 46)

EM78P458/459
OTP ROM
MASK Option. The up-limited operation frequency of crystal/resonator on the different VDDs is listed
in Table 11
Table 12 The Summary of Maximum Operating Speeds
Conditions VDD Fxt max.(MHz)
2.3 4
3.0 8
Two clocks
5.0 20
2. Crystal Oscillator/Ceramic Resonators (XTAL)
EM78P458/459 can be driven by an external clock signal through the OSCI pin as shown in Fig. 18
below.
OSCI
OSCO
Ext.
Clock
EM78P458
EM78P459
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.
OSCI
OSCO
EM78P458
EM78P459
C1
C2
XTAL
RS
Fig. 19 Circuit for Crystal/Resonator
This specification is subject to change without prior notice. 07.01.2003 (V1.3) 46