HD66787 Datasheet, PDF (139/159 Pages) Renesas Technology Corp – 528-channel, One-chip Driver with 262,144-color Display RAM and Power Supply Circuit for Low-temperature Poli-Si TFT (LTPS-TFT) Panels with Incorporat

HD66787
Preliminary
Frame-Frequency Adjustment Function
The HD66787 incorporates frame frequency adjustment function. The frame frequency during the liquid
crystal drive is adjusted by the instruction setting (DIV, RTN) while keeping the oscillation frequency fixed.
Setting the oscillation frequency high in advance allows switching the frame frequency in accordance to the
kind of displayed picture (i.e. moving/still picture). When displaying a still picture, set the frame frequency
low to save power consumption, while setting the frame frequency high when displaying a moving picture
which requires high-speed switching of screens.
Relationship between Liquid Crystal Drive Duty and Frame Frequency
The relationship between the liquid crystal drive duty and the frame frequency is calculated by the
following formula. The frame frequency is adjusted through the instruction setting with the 1-H period
adjustment bit (RTN bit) and the operation clock division bit (DIV bit).
(Formula for the frame frequency)
Frame frequency =
fosc
[Hz]
Clock cycles per raster-row × division ratio × (Line+BP+FP)
fosc: R-C oscillation frequency
Line: number of drive raster-rows (NL bit)
Clock cycles per raster-row: RTN bit
Division ratio: DIV bit
The number of raster-rows for the front porch: FP
The number of raster-rows for the back porch: BP
Calculation Example The maximum frame frequency = 60 Hz
Number of driven raster-rows: 240
1-H period: 16 clock cycles (RTN3-0 = 0000)
Operation clock division ratio: 1 division
fosc = 60 Hz × (0 + 16) clock × 1 division × (240 + 16) lines = 246 (kHz)
In this case, the R-C oscillation frequency becomes 246 kHz. Adjust the external resistor to the R-C
oscillator to 246 kHz.
Rev.0.22, May.23.2003, page 139 of 159