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DIDS-402-2MIO
Para 3-2/3-3
iB
a~iied
to the D/ A converter and used to position the monos cope bearnof!';'
screen when the code of 000 000 is located in the entry register.
The generation
of the, CRT raster is discussed in paragraph 3-4.
3-2 DISPLAY TERMINAL KEYBOARD
The detachable keyboard uses keys which incorporate a magnetically
actuated reed switch.
A diode matrix
is
used to pl"oduce the proper blnal"Y code
from. the single switch closures.
Figure 3-4 shows a simplified keyboard sys-
tem. including a part of the diode matrix.
When the I A I key (for example) is
pressed, voltage's appear on the Xo and Y2 lines, and the coding diodes conduct
, to prOduce output levels on the appropriate lines.
Thus. the binary code fol"
' . I AI is produced by pressing the I A I key:
Gating and delaying logic circuits are provided to jam the code into the readout
register and then into the memory circuit.
3-3 DISPLAY TERMINAL VIDEO AMPLIFICA TION
Monoscope preamplifier A 7 and video amplifier AS amplify the video asso-
ciated with the character being scanned by the monoscope beam and intensity-
modulate the beam of the CRT for viewing.
Each receives its power from low-
voltage power supply A4.
3-8
a.
The monoscope preamplifier has the following signal input/ output:
(1)
The input signal video from the monoscope tube is present
whenever the sweep crOSSeS a part of a character.
The cur-
rent path is from the monoscope target through the input
circuit of the preamplifier and back to the collector of the
monoscope.
(2)
The amplified video output is fed through 75-ohm coax to the
video amplifier.
b.
The video amplifier receives four input signals and a control volt-
age and produces two outputs as explained below:
(1)
A video signal is received from the monoscope preamplifier.
This video corresponds to the character that the monoscope
beam is scanning.
The signal video is amplified and then'
applied to the cathode of CRT V2.
(2)
'Ablanking signal is received from timing board A 14.
This
signal cuts off the video amplifier between characters,
effectively blanking the CRT. during the positioning time re-
, quired for the monoscope beam to switch from one character
to anothe,r and during horizontal and vertical retraces.
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