7477 datasheet(161/361 Pages) RENESAS

161 / 361 page

7470/7471/7477/7478 GROUP USER’S MANUAL

1-154

HARDWARE

1.16 Oscillation circuit

This oscillation circuit can stop and start oscillation.

• XIN-XOUT oscillation circuit ......................... Main clock f(XIN)

• XCIN-XCOUT oscillation circuit .................... Sub-clock f(XCIN)

There are two oscillation circuits (the main clock only in the 7470/7477 group) as shown above. The

clock obtained by dividing a signal input to the clock input pin XIN or XCIN becomes an internal clock

φ+ which is used as a reference for operations.

+: The internal clock

φ varies with the operation modes of the microcomputer.

• Ordinary mode ................ Signal input to the XIN pin divided by 2

• Low-speed mode ............ Signal input to the XCIN pin divided by 2

(2) Oscillation circuit using a ceramic resonator or a crystal oscillator

An oscillation circuit can be formed by connecting a ceramic resonator or a crystal oscillator between

the XIN pin and the XOUT pin and between the XCIN pin and the XCOUT pin.

For a circuit example, refer to “Chapter 2 Application, 2.7 Oscillation Circuit.”

Please ask the oscillator maker for information on circuit constants and then set the value recommended

by the maker.

(3) External clock input circuit

It is also possible to supply a clock to the oscillation circuit from the outside.

As an external clock to be input to the XIN and XCIN pins, use a pulse signal with a duty ratio of 50 %.

At this time, make the XOUT and XCOUT pins open.

For a circuit example, refer to “Chapter 2 Application, 2.7 Oscillation Circuit.”

Note: Because the 7470/7477 group is not provided with the XCIN and XCOUT pins, the sub-clock f(XCIN)

is not available.

7477 Datasheet(PDF) 161 Page - Renesas Technology Corp