ST62T42B ST Microelectronics, ST62T42B Datasheet - Page 48

• Manufacturer Part Number: ST62T42B
• Description: 8-BIT OTP/EPROM MCU WITH LCD DRIVER / EEPROM AND A/D CONVERTER
• Manufacturer: ST Microelectronics

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-
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48
DS1
LF2
0
0
1
1
0
0
0
0
1
1
1
1
DS0
0
1
0
1
LF1
0
0
1
1
0
0
1
1
1/4 mux.ratio
1/1 mux.ratio
1/2 mux.ratio
1/3 mux.ratio
Display Mode
LF0
0
1
0
1
0
1
0
1
Base
f
(Hz)
128
171
256
341
512
LCD
64
85
Frame Frequency f
mux.
ratio
128
171
256
341
512
1/1
64
85
COM1, 2, 3, 4
COM1
COM1, 2
COM1, 2, 3
Active backplanes
Reserved
mux.
ratio
128
171
256
1/2
32
43
64
85
mux.
ratio
114
171
1/3
21
28
43
57
85
F
mux.
ratio
128
(Hz)
1/4
16
21
32
43
64
85
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 V
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.
I
70
60
50
40
30
20
10
LCD
3
( A)
LCDOFF
4
5
6
7
R
R
R
H
H
H
LCD
8
< 4.5V the resis-
9
V
V
V
V
LCD
LCD2/3
SS
LCD1/3
10
VR01367
VR01838
V
LCD
(V)