HT56RB688_13 Datasheet, PDF (42/164 Pages) Holtek Semiconductor Inc – TinyPowerTM A/D Type Smart Card OTP MCU with LCD, DAC, ISO 7816 and USB Interfaces

HT56RB688
TinyPower^TM A/D type Smart Card OTP MCU
with LCD, DAC, ISO 7816 and USB Interfaces
Clock Source
The LCD clock source is the internal clock signal fSUB divided by 8 using an internal divider circuit. The
f_SUB internal clock is supplied by either the internal 32kHz RC oscillator (LIRC) or the external
32.768kHz oscillator (LXT), the choice of which is determined by a configuration option. For proper
LCD operation, this arrangement is provided to generate an ideal LCD clock source frequency of 4kHz.
f_SUB Clock Source
Internal 32kHz oscillator (LIRC)
External 32.768kHz oscillator (LXT)
LCD Clock Frequency
4kHz
4kHz
LCD Clock Source
LCD Driver Output
When the LCDEN bit in the LCDCTRL register is set to 1, the COM and SEG lines will be setup as
LCD driver pins to drive the LCD display.
The number of COM and SEG outputs supplied by the LCD driver and its biasing and duty selections
are dependent upon how the LCD control bits are programmed. The Bias Type is R type and the bias
resistor can be selected using the RSEL1 and RSEL0 bits in the LCDCTRL register.
The nature of Liquid Crystal Displays require that only AC voltages can be applied to their pixels as the
application of DC voltages to LCD pixels may cause permanent damage. For this reason the relative
contrast of an LCD display is controlled by the actual RMS voltage applied to each pixel, which is equal
to the RMS value of the voltage on the COM pin minus the voltage applied to the SEG pin. This
differential RMS voltage must be greater than the LCD saturation voltage for the pixel to be on and less
than the threshold voltage for the pixel to be off. The requirement to limit the DC voltage to zero and to
control as many pixels as possible with a minimum number of connections requires that both a time and
amplitude signal is generated and applied to the application LCD. These time and amplitude varying
signals are automatically generated by the LCD driver circuits in the microcontroller. What is known as
the duty determines the number of common lines used, which are also known as backplanes or COMs.
The duty which is chosen by a control bit to have a value of 1/8 and 1/16 and which equates to a COM
number of 8 and 16 therefore defines the number of time divisions within each LCD signal frame. Two
types of signal generation are also provided, known as Type A and Type B, the required type is selected
via the TYPE bit in the LCDCTRL register. Type B offers lower frequency signals, however lower
frequencies may introduce flickering and influence display clarity.
LCD Control Register - LCDCTRL
Bit
7
6
5
4
Name
TYPE
¾
DTYC
BIAS1
R/W
R/W
¾
R/W
R/W
POR
0
¾
0
0
Bit 7
Bit 6
Bit 5
Bit 4~3
TYPE: LCD Type selection bit
0: Type A
1: Type B
Unimplemented, read as ²0²
DTYC: LCD Duty selection bit
0: 1/8 duty
1: 1/16 duty
BIAS1~BIAS0: LCD Bias selection bits
00: 1/3 bias
01: 1/4 bias
10: 1/5 bias
11: Reserved
3
BIAS0
R/W
0
2
RSEL1
R/W
0
1
RSEL0
R/W
0
0
LCDEN
R/W
0
Rev. 1.10
42
April 15, 2013