HD66108 Datasheet, PDF (36/60 Pages) Hitachi Semiconductor – (RAM-Provided 165-Channel LCD Driver for Liquid Crystal Dot Matrix Graphics)

HD66108
6. Clock and Frame Frequency
An input clock with a 200-kHz to 4-MH frequency can be used for the HD66108T. Note that raising
clock frequency increases current consumption although it reduces busy time and enables high-speed
operations. An optimum system clock frequency should thus be selected within 200 kHz to 4 MHz.
The clock frequency driving the LCD panel (= frame frequency) is usually 70 Hz to 90 Hz. Accordingly,
the HD66108T is so designed that the frequency-division ratio of the input clock can be selected. The
HD66108T generates around 80-Hz LCD frame frequency if the frequency-division ratio is 1. The
frequency-division ratio can be obtained from the following equation.
Ni
=
f_F
f_CLK
×
500
80
× D1
Ni: Frequency-division ratio
f_F: Frame frequency required for the LCD panel (Hz)
f_CLK: Input clock frequency (kHz)
D1: Duty correction value 1
D1 = 1 when multiplexing duty ratio is 1/32, 1/48 or 1/64
D1 = 32/34 when multiplexing duty ratio is 1/34
D1 = 32/36 when multiplexing duty ratio is 1/36
D1 = 48/50 when multiplexing duty ratio is 1/50
D1 = 64/66 when multiplexing duty ratio is 1/66
The frequency-division ratio nearest the value obtained from the above equation must be selected;
selectable frequency-division ratios by internal registers are 2, 1, 1/2, 1/3, 1/4, 1/6, and 1/8.
7. Display Off Function
The HD66108T has a display off function which turns off display by rewriting the contents of the internal
register. This prevents random display at power-on until display memory is initialized.
989