Tandy 102 Service Manual page 40

LCD Segment Driver (HD441
0
2)
M1-M10 (HD44102) on the LCD PCB are segment driver ICs that cause the display data sent from
the main PCB to be memorized in the built-in RAM and automatically generate the LCD drive signal.
One bit of data from the built-in RAM corresponds to one dot of illumination or non-illumination on
the display. The driver outputs are 50 lines.
The transfer of the display data is accomplished by 8-bit parallel data. This IC has several types of
commands. The D/I (H = data, L = command) signal distinguishes between commands and
data. The Tandy 102 has 240 segments each (upper and lower), the segment driver outputs Y41
-Y50 are not used. The power supplied to these ICs, in addition to VDD (+5V) and VEE (-5V), also
includes V1-V6.
VDD and VEE are the power supplies which operates the IC logic. V1 46 operate the LCD driver
signals.
V1 46 are made up by the resistance splitting of R1, R2, R3, R4 and R5. By passing through the
operational amplifier M13, the output impedance of the power supply is lessened.
Capacitors C3, C4, C6, C7 and C8 augment the peak current during LCD illumination.
50 Lines
CS
--
--0 VDD
----o V 1
---o V2
L C D Driver
-- V 3
----0 V4
D
A
D
A
50 Lines
50 Byte (0
Page)
50 Byte ( 1
Page)
U
.
--a VEE
r--0 GND
FRM
me
",vv
o
D
A
50 Byte (2
Page)
CL
M
av
D
A
50 Byte (3
Page)
N
3
3
E
R/W
D/1
ADO
-
7
8
BUSY
Logic CLK(01,02)
Figure 4-23. HD44102 Internal Logic Diagram