ST7712 datasheet(43/113 Pages) SITRONIX

43 / 113 page

ST7712

Ver 2.3

43/113

2007/07/19

7.8 Frame-Frequency Adjustment Function

The ST7712 includes frame frequency adjustment function. While the oscillation frequency is fixed, the frame frequency

during the LC drive can be adjusted by the Frame cycle set instruction (0BH) setting (DIV, RTN). Setting the oscillation

frequency high in advance allows switching the frame frequency in accordance to the kind of picture to display (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 for displaying a moving picture which requires high-speed switching of screens.

7.8.1 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 Frame cycle set instruction (0BH) setting with the 1-H period adjustment bit

(RTN bit) and the operation clock division bit (DIV bit).

Example calculation

Number of drive raster-rows: 132

1-H period: 16 clock cycles (RTN3-0 = 0000)

Operation clock division ratio: 1/1

fosc = 60 Hz × (0 + 16) clock × 1/1 × (132 + 16) lines = 142 (kHz)

In this case, the R-C oscillation frequency becomes 142 kHz. Adjust the external resistor to the R-C oscillator to 142

kHz.

fOSC: R-C oscillation frequency

Line: Number of raster-rows (NL bit)

Clock cycles per raster-row: RTN bit

Division ratio: DIV bit

The No. of raster-rows for the front porch: FP

The No. of raster-row for hte back porch: BP

Frame frequency =

fOSC

Clock cycles per raster-row x division ratio x (Line+BP+FP)

[Hz]

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