HD66420 Datasheet, PDF (37/52 Pages) Hitachi Semiconductor – (RAM-Provided 160 Channel 4-Level Grey Scale Driver for Dot Matrix Graphics LCD)

HD66420
Oscillator
The HD66420 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 23 shows
oscillator connections.
Changing Oscillator
Two oscillators are alternated automatically depending on modes. The resistor between OSC and OSC1 is
used during 32-levels grayscale mode and the resistor between OSC and OSC2 is used during 4-levels
grayscale mode. An external clock must be input from OSC terminal at any modes.
Clock and Frame Frequency
The HD66420 generates the frame frequency by dividing the input clock. Clock frequency is determined
with following equation:
f_OSC = 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 180 kHz for 32-level gray scale display mode, and 18kHz for 4-level gray scale.
Clock
(Open)
(Open)
OSC
HD66420
OSC1
OSC2
Rf2 Rf1
OSC
HD66420
OSC1
OSC2
Rf
(Open)
OSC
HD66420
OSC1
OSC2
a) External clock
b) Dual oscillator
Figure 23 Oscillator Connections
c)Single oscillator
37