HD66727 Datasheet, PDF (57/97 Pages) Hitachi Semiconductor – Low-Power Dot-Matrix Liquid Crystal Display Controller/Driver with Key Scan Function

HD66727
Oscillator Circuit
The HD66727 can either be supplied with operating clock pulses externally (external clock mode) or
oscillate using an internal R-C oscillator and an external oscillator-resistor (internal oscillation mode), as
shown in Figure 31. An appropriate oscillator-resistor must be used to obtain the optimum clock frequency
according to the number of display lines (Table 29). Instruction execution times change in proportion to the
operating clock frequency or R-C oscillation frequency; MPU data transfer rate must be appropriately
adjusted (see Table 23, Instruction List). Figure 32 shows a sample LCD drive output waveform, where 4-
lines are displayed with 1/34 multiplexing duty ratio.
1) When an external clock is used 2) When an internal oscillator is used
Clock
OSC1
HD66727
OSC1
Rf
OSC2
HD66727
The oscillator frequency can be
adjusted by oscillator resistance
(Rf). If Rf is increased or power
supply voltage is decreased, the
oscillator frequency decreases.
Figure 31 Oscillator Circuit
Table 29 Oscillation Frequency and LCD Frame Frequency
Item
Multiplexing duty ratio
R-C oscillation
frequency
(recommended value)
1-line drive frequency
Frame frequency
1-Line Display
(NL1, NL0 = 00)
1/10
40 kHz
0.66 kHz
67 Hz
2-Line Display
(NL1, NL0 = 01)
1/18
80 kHz
1.3 kHz
74 Hz
3-Line Display
(NL1, NL0 = 10)
1/26
120 kHz
2.0 kHz
77 Hz
4-Line Display
(NL1, NL0 = 11)
1/34
160 kHz
2.7 kHz
78 Hz
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