EM78F651NAMSSLASHNAMJ datasheet(39/58 Pages) EMC

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EM78F651N

8-Bit Microcontroller

Product Specification (V1.1) 10.20.2006

• 35

(This specification is subject to change without further notice)

6.9 Oscillator

6.9.1 Oscillator Modes

The device can be operated in four different oscillator modes, such as Internal RC

oscillator mode (IRC), External RC oscillator mode (ERC), High Crystal oscillator

mode (HXT), and Low Crystal oscillator mode (LXT). User can select one of such

modes by programming OSC2, OCS1 and OSC0 in the Code Option register.

Table11 depicts how these four modes are defined.

The up-limited operation frequency of the crystal/resonator on the different VDD is

listed in Table 11

Table 11 Oscillator Modes defined by OSC2 ~ OSC0

Mode

OSC2

OSC1

OSC0

XT (Crystal oscillator mode)

HXT (High Crystal oscillator mode)

LXT1 (Low Crystal 1 oscillator mode)

LXT2 (Low Crystal 2 oscillator mode)

IRC mode, OSCO (P54) act as I/O pin

IRC mode, OSCO (P54) act as RCOUT pin

ERC mode, OSCO (P54) act as I/O pin

ERC mode, OSCO (P54) act as RCOUT pin

NOTE

1. Frequency range of HXT mode is 20MHz ~ 6MHz.

2. Frequency range of XT mode is 6MHz ~ 1MHz.

3. Frequency range of LXT1 mode is 1MHz ~ 100kHz.

4. Frequency range of XT mode is 32kHz.

Table 12 Summary of Maximum Operating Speeds

Conditions

VDD

Max Fxt. (MHz)

2.5

4.0

3.0

8.0

Two cycles with two clocks

5.0

20.0

6.9.2 Crystal Oscillator/Ceramic Resonators (Crystal)

The EM78F651N can be driven by an external clock signal through the OSCI pin as

shown in Fig 6-10 below.

OSCI

OSCO

EM78F651N

Ext. Clock

Fig. 6-10 Circuit for External Clock Input

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