HD66750 Datasheet, PDF (79/96 Pages) Hitachi Semiconductor – 128 x 128-dot Graphics LCD Controller/Driver with Four-grayscale Functions

HD66750/1
Partial-display-on Function
The HD66750/1 can program the liquid crystal display drive duty ratio setting (NL3-0 bits), the liquid
crystal display drive bias value selection (BS2-0 bits), the boost output level selection (BT1-0 bits), and the
contrast adjustment (CT5-0 bits). For example, when the 128 x 120-dot screen is normally displayed with
a 1/120 duty ratio, the HD66750/1 can selectively drive only the center of the screen or the top of the screen
by combining these register functions and the centering display function (CN bit). This is called partial-
display-on. Lowering the liquid crystal display drive duty ratio reduces the liquid crystal display drive
voltage, thus reducing internal current consumption. This is suitable for a 16 raster-row display (1/16
duty ratio) of a calendar or time in the system-standby state, or the display of only graphics icons
(pictograms) at the top of the screen, which enables continuous display with minimal current consumption.
The non-displayed lines are constantly driven by the unselected level voltage, thus turning off the LCD for
these lines.
In general, lowering the liquid crystal display drive duty ratio decreases the optimum liquid crystal display
drive voltage and liquid crystal display drive bias value. This reduces output multiplying factors in the
booster and greatly controls consumption current.
Table 26 Partial-display-on Function (1/120-duty Normal Drive)
Item
Normal Display
Partial-on Display (Limited to Four-line Display)
LCD screen
128 x 120 dots
128 x 16 dots only on 128 x 16 dots only at the
the center of the screen top of the screen
LCD drive position Not necessary
shift
(CN = 0)
Necessary
(CN = 1)
Not necessary
(CN = 0)
LCD drive duty ratio 1/120 (NL3 to 0 = 1110) 1/16 (NL3 to 0 = 0001) 1/16 (NL3 to 0 = 0001)
LCD drive bias
value (optimum)
1/11 (BS2 to 0 = 000) 1/5 (BS2 to 0 = 110) 1/5 (BS2 to 0 = 110)
LCD drive voltage*
13.5 V to 15.5 V
(precisely adjustable
using CT5 to 0)
4 V to 5 V
(precisely adjustable
using CT5 to 0)
4 V to 5 V
(precisely adjustable
using CT5 to 0)
Boosting output
multiplying factor
Six times (BT1 to 0 = 10) Two times (BT1 to 0 = Two times (BT1 to 0 =
00)
00)
Frame frequency
(fosc = 70 kHz)
68 Hz
68 Hz
68 Hz
Note: The LCD drive voltage depends on the LCD materials used. Since the LCD drive voltage is high
when the LCD drive duty ratio is high, a low duty ratio enables low-power consumption.
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