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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.
Main clock supplied from the X
Main clock supplied from the X
Clock from the LC or RC supplied from the pins OSC1 and OSC2.
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 00ED
the main clock, set the oscillation frequency to 8 MHz.
CRT Clock Selection Register
b7 b6 b5 b4 b3 b2 b1 b0
0
0
0
0
0
0
Note: It is necessary to connect other ceramic resonator or quartz-crystal oscillator across the pins X
Fig. 2.11.19 CRT clock selection register
2-88
pin
IN
pin divided by 1.5
IN
CRT clock selection register (CK) [Address 00ED
B
Name
b1
b0
0, 1 CRT clock
selection bits
The clock for display is supplied by connecting RC
1
0
(CK0,CK1)
or LC across the pins OSC1 and OSC2.
0
1
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
1
0
case, pins OSC1 and OSC2 are also used
as input ports P3
1
1
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)
2
Fix these bits to "0."
to
7
7220 Group User's Manual
]
16
Functions
Functions
CRT oscillation
frequency
= f(X
)
IN
CRT oscillation
frequency
and P3
respectively.
3
4
= f(X
)/1.5
IN
). When selecting
16
After reset R W
0
R W
0
R W
and X
.
IN
OUT
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