EM78P257AM datasheet(47/91 Pages) EMC

47 / 91 page

EM78P257

OTP ROM

This specification is subject to change without prior notice.

07.27.2004 (V1.4)

ERC(External RC oscillator mode)

HXT(High XTAL oscillator mode)

LXT(Low XTAL oscillator mode)

<Note> The transient point of system frequency between HXT and LXT is around 400 KHz.

Table 16 The summary of maximum operating speeds

Conditions

VDD

Fxt max.(MHz)

2.3

3.0

Two clocks

5.0

2. Crystal Oscillator/Ceramic Resonators(XTAL)

EM78P257A/B can be driven by an external clock signal through the OSCI pin as shown in Fig.18 below.

OSCI

OSCO

EM78P257A/B

Fig. 18 Circuit for External Clock Input

In 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 thing applies whether it is in the HXT mode or in the LXT mode.

Table 17 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.

OSCI

EM78P257A/B

OSCO

XTAL

Fig. 19 Circuit for Crystal/Resonator

EM78P257AM Datasheet(PDF) 47 Page - ELAN Microelectronics Corp