ST6246 STMICROELECTRONICS [STMicroelectronics], ST6246 Datasheet - Page 48

• Manufacturer Part Number: ST6246
• Description: 8-BIT OTP/EPROM MCU WITH LCD DRIVER, EEPROM AND A/D CONVERTER
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

ST62T46B/E46B
4.5 LCD CONTROLLER-DRIVER
On-chip LCD driver includes all features required
for LCD driving, including multiplexing of the com-
mon plates. Multiplexing allows to increase display
capability without increasing the number of seg-
ment outputs. In that case, the display capability is
equal to the product of the number of common
plates with the number of segment outputs.
A dedicated LCD RAM is used to store the pattern
to be displayed while control logic generates ac-
cordingly all the waveforms sent onto the segment
or common outputs. Segments voltage supply is
MCU supply independant, and included driving
stages allow direct connection to the LCD panel.
The multiplexing ratio (Number of common plates)
and the base LCD frame frequency is software
configurable to achieve the best trade-off con-
trast/display capability for each display panel.
The 32KHz clock used for the LCD controller is
derivated from the MCU’s internal clock and there-
fore does not require a dedicated oscillator. The
division factor is set by the three bits HF0..HF2 of
the LCD Mode Control Register LCDCR as sum-
marized in Table 15 for recommanded oscillator
Figure 25. LCD Block Diagram
48/72
384
(When available)
OSC 32KHz
f
int
VLCD
VOLTAGE
DIVIDE R
VLCD VLCD
1/3
SELECTION
CLOCK
2/3
32KHz
CONTROLLER
BACKPLAN ES
COMMON
DRIVE R
quartz values. In case of oscillator failure, all seg-
ment and common lines are switched to ground to
avoid any DC biasing of the LCD elements.
Table 15. Oscillator Selection Bits
Notes:
1.
defined in this table cause the LCD to operate at a
reference frequency different from 32.768KHz, ac-
cording to division factor of Table 15.
2.
frequency lower than 32.768KHz as the clock su-
pervisor circuit may switch off the LCD peripheral
if lower frequency is detected.
Oscillator
1.048MHz
2.097MHz
4.194MHz
8.388MHz
MCU
f
OSC
The usage f
It is not recommended to select an internal
REGISTER
CONTROL
HF2 HF1 HF0
0
0
1
1
1
DATA BUS
0
1
0
0
1
OSC
SEGMENT
SEGMENTS
DRIVER
values different from those
0
1
0
1
0
Clock disabled: Display off
32
64
128
256
Division Factor
RAM
LCD
VR02099