ST62T42B datasheet(48/68 Pages) STMICROELECTRONICS

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ST62T42B/E42B

LCD CONTROLLER-DRIVER (Continued)

5.4.1 Multiplexing ratio and frame frequency

setting

Up to 4 common plates COM1..COM4 can be

used for multiplexing ratio ranging from 1/1 to 1/4.

The selection is made by the bits DS0 and DS1 of

the LCDCR as shown in the Table 19.

Table 19. Multiplexing ratio

If the 1/1 multiplexing ratio is chosen, LCD seg-

ments are refreshed with a frame frequency Flcd

derived from 32Khz clock with a division ratio de-

fined by the bits LF0..LF2 of the LCDCR.

When a higher multiplexing ratio is set, refreshment

frequency is decreased accordingly (Table 20).

Table 20. LCD Frame Frequency Selection

5.4.2 Segment and common plates driving

LCD panels physical structure requires precise

timings and stepped voltage values on common

and segment outputs. Timings are managed by

the LCD controller, while voltages are derivated

from the VLCD value through internal resistive di-

vision. This internal divider is disabled when the

LCD driver is OFF in order to avoid consumption

on VLCD pin.

The 1/3 VLCD and 2/3 VLCD values used in 1/1,

1/3 and 1/4 multiplexing ratio modes are internally

generated and issued on external pins, while 1/2

VLCD value used in 1/2 mode is obtained by exter-

nal connection of the 1/3VLCD and 2/3VLCD pins

(Figure 25).

Figure 25. Bias Config for 1/2 Duty

Figure 26. Typical Current consumption on

VLCD Pin (25

°C, no load, fLCD=512Hz, mux=1/3-

1/4)

Note: For display voltages VLCD < 4.5V the resis-

tivity of the divider may be too high for some appli-

cations (especially using 1/3 or 1/4 duty display

mode). In that case an external resistive divider

must be used to achieve the desired resistivity.

DS1

DS0

Display Mode

Active backplanes

1/4 mux.ratio

COM1, 2, 3, 4

1/1 mux.ratio

COM1

1/2 mux.ratio

COM1, 2

1/3 mux.ratio

COM1, 2, 3

LF2

LF1

LF0

Base

fLCD

(Hz)

Frame Frequency fF (Hz)

1/1

mux.

ratio

1/2

mux.

ratio

1/3

mux.

ratio

1/4

mux.

ratio

128

171

256

128

341

171

114

512

256

171

128

Reserved

VLCD

VLCD1/3

VSS

VLCD2/3

LCDOFF

VR01367

ILCD(µA)

VLCD(V)

345

VR01838

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