Tandy 102 Service Manual page 41

LCD Waveform
In order to drive the liquid-crystal element by the 1/32 duty line-sequential drive method, the LCD of
the Tandy 102 makes sequential selection of the 32 scanning electrodes.
For each dot, the display signal passes through the signal electrode and is applied 32 times for one
display.
At this point, the signal is necessary at each dot only one time. The signals for the other 31
times correspond to other dots on the same signal electrode.
The maximum voltage applied to common electrode and segment electrode is the potential
difference between V1 and V2.
In addition, "a" is the bias coefficient which determines, from the standpoint of contrast, the
maximum ratio between the illumination voltage and the non-illumination voltage.
When that ratio is the greatest in relation to the effective ON and OFF voltages, a = 6.66.
Thus, for V1, V2, V3, V4, V5 and V6:
V1 = VEE(-5V)
V2 = V (about 0-4V)
V3 = 2/aV
V4 =
(1 -2/a)V
V5 = (1-1 /a)V
V6 = a/aV
VO
ID
VO
ID
COMMON
LINE
Q_UvOP
I
I I
2
VOP
Non-illumination
2
VO
ID
Segment Line
Z VOP
2 vOP
VO
ID
illumination
Segment Line
Figure 4-24. LCD Waveform
4-23