GMS81C7216 Datasheet, PDF (72/121 Pages) List of Unclassifed Manufacturers – 8-BIT SINGLE-CHIP MICROCONTROLLERS

GMS81C7208/7216
COM0 pin
one frame
(at 1/4 duty, 1/3 bias)
LCD Port Selection
Segment pins are also used for normal I/O pins. The LCD port se-
lection register LPMR is used to set Rn pin for ordinary digital in-
put. Refer to LPMR register as shown in Figure 18-2.
Bias Resistor
To operate LCD, built-in Bias resistor dividing V_DD to V_SS
section into several stages generates necessary voltage.
The BTC (Bit 6 of LCR) switches Transistor supplying voltage to
serially connected Bias resistor. If it is ‘1’, it turns on, and if it is
‘0’, it turns off. The LCD drive voltage (V_CL2) is given by the dif-
ference in potential (V_DD-V_CL2) between pins V_DD and V_CL2.
Therefore, when the MCU operating voltage is 5V and LCD drive
voltage are the same, the Bias pin is connected to the V_CL2 pin as
shown in (a) of Figure 18-5.
MCU Internal
V_DD
BTC
2R
R
BRC
R
R
V_SS
MCU Internal
V_DD
BTC
BIAS
2R
VCL2 _{Two pins are connected}
each other
R
VCL1
VCL2=5V
VCL1=3.33V
R
VCL0=1.67V
VCL0
R
V_SS
BRC
BIAS
VCL2 Short two pins
each other externally
VCL1
VCL0
VCL2=5V
VCL1=2.5V
VCL0=2.5V
BTC = “1” BRC = “1”
(a) Internal, Static or 1/3 Bias
BTC = “1” BRC = “1”
(b) Internal, Static or 1/2 Bias
Typ. R=65kΩ
Figure 18-4 Application Example of 5V LCD Panel
When require supply 3V output to the LCD, the voltage of V_CL2
becomes 3V as shown in Figure 18-5. Because V_DD is down to
3V through internal 2R resistor.
The LCD light only when the difference in potential between the
segment and common output is ±VCL, and turn off at all other
times. During reset, the power switch of the LCD driver is turned
off automatically, shutting off the VCL voltage.
68
FEB. 2005 Ver 1.04