Lcd Voltage Source And Biasing - Holtek HT67F2350 Manual

HT67F2350/HT67F2360
HT67F2370/HT67F2390
Advanced A/D Flash MCU with LCD & EEPROM
LCDC2 Register
Bit 7
Name —
R/W —
POR —
Bit 7~3 Unimplemented, read as "0"
Bit 2~1 DTC1~DTC0: LCD duty selection
00: 1/4 duty – COM0~COM3 used, for both R and C type.
01: 1/6 duty – COM0~COM5 used, for both R and C type.
10: 1/8 duty – COM0~COM7 used, for R type only.
11: Unimplemented
The unused COM pin can be configured as other pin-shared functions using the
corresponding pin-shared selection register.
Bit 0 BIAS: LCD bias selection
0: 1/3 bias – for both R and C types
1: 1/4 bias – for R type only
The 1/3 bias selection can be used for both R and C types while the 1/4 bias selection
can only be used for R type. It is recommended to use the 1/4 bias selection for the 1/8
duty configuration.

LCD Voltage Source and Biasing

The time and amplitude varying signals generated by the LCD Driver function require the generation
of several voltage levels for their operation. The devices can have either R type or C type biasing
selected via a software control bit named RCT. Selecting the C type biasing will enable an internal
charge pump circuitry.
R Type Biasing – 1/3 Bias & 1/4 Bias
For R type biasing an external LCD voltage source must be supplied on pin PLCD to generate the
internal biasing voltages. This could be the microcontroller power supply V
source equal to or less than V
and V are utilised. For the R type 1/4 bias scheme, five voltage levels V
C
utilised. The voltage V
V varying from 8/16 V
PLCD
1/8 duty selection.
Different values of internal bias resistors can be selected using the RSEL2~RESEL0 bits in the
LCDC0 register. This along with the voltage on pin PLCD will determine the bias current. The
VMAX pin should be connected to the VDD pin and the available maximum voltage applied to the
PLCD pin is equal to V
if R type biasing is used.
Bias Selection
Rev. 1.60
6 5 4
— — —
— — —
— — —
. For the R type 1/3 bias scheme, four voltage levels V
DD
is selected by the PLCD3~PLCD0 bits to be equal to a specific ratio of
A
to V . Note that the 1/4 bias type is recommended to be used for
PLCD PLCD
. Note that no external capacitors or resistors are required to be connected
DD
1/3 Bias V =8/16V ~ V
A PLCD
1/4 Bias V =8/16V ~ V
A PLCD
R Type Bias Voltage
227
3 2
— DTYC1 DTYC0
— R/W R/W
— 0
or some other voltage
DD
, V , V
SS A
Bias Voltage
; V =2/3V ; V =1/3V .
PLCD B A C A
; V =3/4V ; V =2/4V ; V =1/4V
PLCD B A C A D
1 0
BIAS
R/W
0 0
, V , V
SS A B
, V and V are
B C D
.
A
May 16, 2019