7220 datasheet(115/303 Pages) RENESAS

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2-88

7220 Group User’s Manual

FUNCTIONAL DESCRIPTION

2.11 CRT display function

2.11.9 Clock for display

As a clock for display to be used for CRT display, it is possible to select one of the following 4 types.

q Main clock supplied from the XIN pin

q Main clock supplied from the XIN pin divided by 1.5

q Clock from the LC or RC supplied from the pins OSC1 and OSC2.

q Clock from the ceramic resonator or quartz-crystal oscillator supplied from the pins OSC1 and OSC2.

This clock for display can be selected by the CRT clock selection register (address 00ED16). When selecting

the main clock, set the oscillation frequency to 8 MHz.

Fig. 2.11.19 CRT clock selection register

b7 b6 b5 b4 b3 b2 b1 b0

CRT clock selection register (CK) [Address 00ED

Name

Functions

After reset R W

CRT Clock Selection Register

0, 1 CRT clock

selection bits

(CK0,CK1)

Since the main clock is used as the clock for

display, the oscillation frequency is limited.

Because of this, the character size in width

(horizontal) direction is also limited. In this

case, pins OSC1 and OSC2 are also used

as input ports P33 and P34 respectively.

The clock for display is supplied by connecting the

following across the pins OSC1 and OSC2.

• a ceramic resonator only for CRT display and a feedback resistor

• a quartz-crystal oscillator only for CRT display and a feedback

resistor (Note)

The clock for display is supplied by connecting RC

or LC across the pins OSC1 and OSC2.

Functions

CRT oscillation

frequency

= f(XIN)

CRT oscillation

frequency

= f(XIN)/1.5

Note: It is necessary to connect other ceramic resonator or quartz-crystal oscillator across the pins X

Fix these bits to “0.”

and XOUT.

]

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