HD66421 Datasheet, PDF (32/46 Pages) Hitachi Semiconductor – (RAM-Provided 160 Channel 4-Level Grey Scale Driver for Dot Matrix Graphics LCD)

Preliminary
Rev. 1.1E '99.02.10
HD66421
Oscillator
Clock and Frame Frequency
The HD66421 incorporates two sets of R-C
oscillator for two display modes: OSC-OSC1
oscillator is used for 32-levels gray scale
display mode and OSC-OSC2 oscillator for
4-levels gray scale display mode. If the internal
oscillator is not used, an appropriate clock
signal must be externally input through the
OSC pin. In this case, the OSC1 and OSC2 pins
must be left unconnected. Oscillation resister
must be placed near LSI, because if capacitance
exists between OSC and OSC1 oscillator may
not work properly. Figure 30 shows oscillator
connections.
The HD66421 generates the frame frequency by
dividing the input clock. Clock frequency is
determined with following equation:
fOSC = N * (Duty ratio) * (Frame frequency)
N: 31 for 32-level gray scale display mode
3 for 4-level gray scale display mode
The frame frequency is usually 70 to 90 Hz;
when the frame frequency is 70 Hz, for example,
the input clock frequency will be 220 kHz for
32-level gray scale display mode, and 18kHz for
4-level gray scale.
Changing Oscillator
LCD Driving Alternating Cycle
Two oscillators are alternated automatically
depending on modes. An external clock must be
input from OSC terminal at any modes.
AC voltage needs to be applied to liquid crystals
to prevent deterioration due to DC voltage. This
alternated cycle is determied by setting
Alernating cycle register (R16); 7, 11, 13lines or
flame.
Clock
(Open)
(Open)
OSC
HD66421
OSC1
OSC2
Rf2 Rf1
OSC
HD66421
OSC1
OSC2
Rf
(Open)
OSC
HD66421
OSC1
OSC2
a) External clock
b) Dual oscillator
Figure 30 Oscillator Connections
c)Single oscillator
Table 8 LCD alternative drive cycle
CM1
0
0
0
0
CM0
0
0
0
0
Alternative
Cycle
Frame
7 lines
11 lines
13 lines
32