HD66781 Datasheet, PDF (178/196 Pages) Renesas Technology Corp – 720-channel Source Driver for a-Si TFT/Low Temperature Poly-Si TFT Panels with 262,144-color display RAM

HD66781
Preliminary
Frame-Frequency Adjustment Function
The HD66781 incorporates frame frequency adjustment function. The frame frequency during the liquid
crystal drive is adjusted by the instruction setting (DIVI, RTNI) while keeping the oscillation frequency
fixed.
By setting the oscillation frequency high in advance, it becomes possible to switch 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 screen switching.
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 by the instruction setting with the 1-H period
adjustment bit (RTNI bit) and the operation clock division bit (DIVI bit).
(Formula for the frame frequency)
fosc
Frame frequency =
[Hz]
Clock cycles per raster-row × division ratio × (Line+BP+ FP)
fosc
Clock cycles per raster-row
Division ratio
Line
Front Porch
Back Porch
: R-C oscillation frequency
: RTNI bits
: DIVI bit
: number of drive raster-rows (NL)
: FP bits
: BP bits
Calculation Example The maximum frame frequency = 60 Hz
Number of drive raster-row
1-H period
Operation clock division ratio
: 320
: 16 clock cycles (RTNI[4:0] = 2’h10)
: 1 division
fosc = 60 Hz × 16 clocks × 1 division × (320+2+14) lines = 323 (kHz)
In this case, the R-C oscillation frequency becomes 323 kHz. Adjust the value of external resistor for R-C
oscillator to set the frequency 323kHz.
Rev.0.5, July.31.2003, page 178 of 196