EM78468
8-BIT Microcontroller
4.9 LCD Driver
This LSI can drive LCD of up to 32 segments and 4 commons that can drive 4*32 dots
totally. LCD block is made up of LCD driver, display RAM, segment output pins, common
output pins, and LCD operating power supply pins. This circuit works on normal mode,
green mode and idle mode. The LCD duty; bias; the number of segment; the number of
common and frame frequency are determined by the LCD controller register.
The basic structure contains a timing control that uses a subsystem clock to generate the
proper timing for different duty and display accesses. The R9 register is a command
register for LCD driver which includes LCD enable/disable, bias (1/2 and 1/3), duty (1/2,
1/3, 1/4), and LCD frame frequency control. The register RA is an LCD contrast and LCD
RAM address control register. The register RB is an LCD RAM data buffer. LCD booster
circuit can change operation frequency to improve VLCD2 and VLCD3 drive capability.
The control register is explained as follows.
R9/LCDCR (LCD Control Register)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
BS
DS1
DS0
LCDEN
--
LCDTYPE LCDF1
LCDF0
Bit 7 (BS): LCD bias select bit, 0/1=>(1/2 bias) / (1/3 bias)
Bit 6 ~ 5 (DS1 ~ DS0): LCD duty select
DS1
DS0
0
1
X
LCD Duty
1/2 duty
1/3 duty
1/4 duty
0
0
1
Bit 4 (LCDEN): LCD enable bit: 0/1 -> LCD circuit disable/enable
When LCD function is disabled, all common/segment output is set to ground (GND) level
Bit 3: Not used
Bit 2 (LCDTYPE): LCD drive waveform type select bit
LCDTYPE = “0”: “A” type waveform
LCDTYPE = “1”: “B” type waveform
Bit 1 ~ 0(LCDF1 ~ LCDF0): LCD frame frequency control bits
LCD frame frequency (e.g. Fs=32.768KHz)
LCDF1
LCDF0
1/2 duty
1/3 duty
1/4 duty
0
0
1
1
0
1
0
1
Fs/(256*2)=64.0
Fs/(280*2)=58.5
Fs/(304*2)=53.9
Fs/(232*2)=70.6
Fs/(172*3)=63.5
Fs/(188*3)=58.0
Fs/(204*3)=53.5
Fs/(156*3)=70.0
Fs/(128*4) =64.0
Fs/(140*4) =58.5
Fs/(152*4) =53.9
Fs/(116*4) =70.6
Fs: sub-oscillator frequency
42 •
Product Specification (V1.1) 04.11.2005
(This specification is subject to change without further notice)
ELAN [ ELAN MICROELECTRONICS CORP ]
