7220 Datasheet, PDF (263/303 Pages) Renesas Technology Corp – 8-BIT SINGLE-CHIP MICROCOMPUTER

APPENDIX
6.7 Control registers
CRT Clock Selection Register
b7 b6 b5 b4 b3 b2 b1 b0
000000
CRT clock selection register (CK) [Address 00ED16]
B
Name
Functions
0, 1 CRT clock ^{b1 b0}
Functions
selection bits 1 0 The clock for display is supplied by connecting RC
(CK0,CK1)
or LC across the pins OSC1 and OSC2.
After reset R W
0
RW
0 1 Since the main clock is used as the clock for _{CRT oscillation}
display, the oscillation frequency is limited. _frequency
Because of this, the character size in width _{= f(XIN)}
(horizontal) direction is also limited. In this
1 0 _{case, pins OSC1 and OSC2 are also used} CRT oscillation
as input ports P33 and P34 respectively.
frequency
= f(XIN)/1.5
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
0
RW
Note: It is necessary to connect other ceramic resonator or quartz-crystal oscillator across the pins XIN and XOUT.
Fig. 6.7.21 CRT clock selection register
Address 00ED16
6-44
7220 Group User’s Manual