HT67F60 datasheet(210/242 Pages) HOLTEK

210 / 242 page

Rev. 1.50

210

March 06 , 2012

Rev. 1.50

211

March 06 , 2012

HT67F30/HT67F40/HT67F50/HT67F60

TinyPowerTM A/D Flash Type 8-Bit MCU with LCD & EEPRO

LCD Reset Function

The LCD has an internal reset function that is an OR function of the inverted LCDEN bit in the

LCDCTRL register and the Sleep function. The LCD reset signal is active high. The LCDENB

signal is the inverse of the LCDEN bit in the LCDCTRL register.

Reset LCD = (Sleep Mode AND LCDEN) OR LCDENB.

LCDEN

Sleep Mode

Reset LCD

Off

√

Off

√

LCD Reset Function

Clock Source

The LCD clock source is the internal clock signal, fSUB, divided by 8, using an internal divider

circuit. The fSUB internal clock is supplied by either the LIRC or LXT oscillator, 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.

fSUB Clock Source

LCD Clock Frequency

LIRC

4kHz

LXT

4kHz

LCD Clock Source

LCD Driver Output

The number of COM and SEG outputs supplied by the LCD driver, as well as its biasing and duty

selections, are dependent upon how the LCD control bits are programmed. The Bias Type, whether

C or R type is selected via a configuration option.

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 1/2, 1/3, 1/4 etc and which equates to a COM number of

2, 3, 4 etc, 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.

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