Control Data Corporation INFORMATION SYSTEMS TERMINAL II Hardware Maintenance Manual page 111

OPERATORS PANEL
This panel consists of 2 PCB attached to the bezel/keyboard
cover .. Attached to it are: the tone generator (alarm),
reset ·switch, six LEOs, DATA/TALK switch, and six rocker
switches. The brightness control potentiometer also
attaches to the bezel/keyboard cover, but is not part of
the operator's panel PCB.
TOUCHPANEL
The touchpanel assembly consists of the touchpanel and con-
nectors. The scanning and touch detection logic is part of
the basic unit and is in the controller PCB.
It consists of a 16 by 16 matrix of touch-sensitive areas
installed adjacent to the display surface. Pressure
applied to the touchpanel/display surface interrupts the X
and Y scanning mechanism. When a touch is detected, the
interface logic captures the intersecting X/Y coordinates
for further processing.
The touchpanel interface, as present at the internal con-
troller board connector AJ3, consists of the signals listed
in table 4-10. The 16 Y signal lines are connected to the
16 touchpanel rows (on the mylar of the touchpanel assem-
bly).
The 16 X signal lines are connected to the 16 touch-
panel columns (on the glass of the touchpanel assembly).
The characteristics of the touchpanel are such that if
pressure is applied to a particular cell, the intersecting
column signal line and row signal line are effectively
shorted together. The touchpanel interface logic on the
controller board operates basically as follows. The upper
4 outputs of an initially free-running 8-bit counter are
fed into a 1-of-16 decoder, which then sequentially drives
each column signal line to a logical low while leaving the
others high. During the excitation of each column signal
line, the lower 4 outputs of the counter are employed, via
a 16-input multiplexer, to sequentially select each row
signal line for sampling. Upon detection of a logical low
row signal line, the controller logic:
1. Delays (debounces) the signal
2. Stops the counter
3. Sets the Touchpanel Data Ready status/interrupt
82100083 B 4-49