EM78P447S
OTP ROM
4.7 Oscillator
1. Oscillator Modes
The EM78P447S can operate in three different oscillator modes, i.e., high XTAL (HXT) oscillator mode, low XTAL (LXT)
oscillator mode, and External RC oscillator mode (ERC) oscillator mode. User can select one of them by programming MS,
HLF and HLP in the Code Option Register. Table 7 depicts how these three modes are defined.
The maximum limit for operational frequencies of crystal/resonator under different VDDs is listed in Table 8.
Table 8 Oscillator Modes Defined by MS and HLP
Mode
MS
0
HLF
*X
1
HLP
*X
*X
0
ERC(External RC oscillator mode)
HXT(High XTAL oscillator mode)
LXT(Low XTAL oscillator mode)
1
1
0
<Note>
1. X, Don’t care
2. The transient point of system frequency between HXT and LXY is around 400 KHz.
Table 9 The Summary of Maximum Operating Speeds
Conditions
VDD
2.3
Fxt max.(MHz)
4.0
8.0
20.0
Two cycles with two clocks
3.0
5.0
2. Crystal Oscillator/Ceramic Resonators(XTAL)
EM78P447S can be driven by an external clock signal through the OSCI pin as shown in Fig. 10 below.
In most applications, Pin OSCI and Pin OSCO can be connected with a crystal or ceramic resonator to generate
oscillation. Fig. 11 depicts such circuit. The same thing applies whether it is in the HXT mode or in the LXT mode. Table 9
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.
This specification is subject to change without prior notice.
24
06.25.2003 (V1.1)
ELAN [ ELAN MICROELECTRONICS CORP ]
