Lcd - Tandy 102 Service Manual

LCD
The LCD used in the Tandy 102 is composed of electrodes in a matrix arrangement (64 common
signals and 480 segment signals ) This part is subdivided into the following three sections:
• LCD Common Driver
• LCD Segment Driver
• LCD Waveform
For a more detailed description of how the LCD operates and its basic construction, refer to
Appendix C of this manual.
LCD Common Driver (HD44103)
The Tandy 102 uses two common driver ICs: M11 and M12. M11 controls the upper half of the LCD
screen and M12 controls the lower half of the LCD screen. M11 and M12 are cascade connected,
and a 1/32-duty backscan signal is made. By using C5 and R10 connected to the C and R terminals
of M11, a timing signal is generated, which controls M12. M11 can be considered to be the master
IC and M12 the slave.
The FRM signal defines the periodic frequency of one-screen display, and determines 70 Hz for the
Tandy 102.
The MB signal is used for changing the driver signal to AC, because the continuous application of
DC to the LCD would shorten the LCD element life.
The CL1 signal is used for the shift clock of the internal shift register.
The 01 and 02 signals are the clock signals for the HD44102 RAM operation.
2OLines
LCD Driver
DL Logic
CL
SHL
FCS
FRM
M Logic
Rf
Cf
OSC
20Lines
20Steps 8i-Directional
Shift Register
Divider Divider
CLK Logic
(01,02)
Frame Frequency Duty Selector
Selector
Logic DR
-f--0 VDD
-00--0
V1
+--o V 2
. --o V 5
----o V 6
--*-
--o VEE
Figure 4-22. HD44103 Internal Logic Diagram