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DIDS-402-2AM13
When a character code is entered into the CE register from any of the
input sources, a com.p1ete 7-bit code is available for transfer during CTS.
The
code is coupled from the set output of each CE register and applied in parallel to
the input of each flip-flop of the CR register.
During 2CTS, the digital code held
in the CE register is clocked into the CR register.
From the CR register, the
7-bit code is divided into two segments consisting of one 4-bit segment and one
3-bit segment.
These segments are coupled to the Monoscope Deflection
Amplifier
(A3)
and direct t",
~
monoscope beam to a specific character on the
monoscope target.
In addition to accepting digital codes from the CE register, the CR :register
may be jammed to contain specific codes when special characters are decoded
in the CE register.
These alternate codes are de scribed as follows:
a.
Cursor Character - T1!.e cursor symbol displayed on the CRT screen is
optionally the symbol:: or..J.
The
J
cursor symbol is developed
on the video amplifier board when the cursor bit appears in the
cursor-located flip-flop.
The
~
cursor symbol is developed by
directing the monoscope beam to the cursor character position
on the monoscope target.
This is accomplished in the foHowi ng
manner:
When the
cursor symbol is employed, the symbol is alternately
displayed instead of the character with which it is associated.
This
requires connecting a wire between terminals Band C on the display
logic board.
The 3-Hz pulse recurs once every 0.333 ms or
20 times/frame, while the cursor appears in the CE register only
once/frame.
When the cursor and the 3-Hz l"ulse appear in coinci-
dence, NAND- gate
A69.
11 is enabled and flip-flop A 75.9 is set on
the following phase 2 pulse.
This jams the cursor code into the CR
register so that the cursor symbol
(§)
is displayed instead of the
character as sociated with the cursor.
Due to the random nature of
the cursor [a
1.
6
-f.LS
pulse occurring once every 16 ms and a 3-Hz
pulse (0.333 ms) occurring in coincidence], the character code is
displayed several times as compared to each time the cursor is
displayed.
The high refresh rate of 63 Hz, however, produces a
visual effect of the two characters alternating on the screen.
b.
DEL Character - When the delay line is erased, consecutive l's
are inserted into each of the 1040 character.positions.
These
characters exist in the delay line until other codes are entered
to replace them.
Each time a DEL character (1111111) appears in
the CE register, a code conversion is enabled through the DEL
decode
A64.8.
When the DEL decode is enabled, the code 1111111 (shifted into the
CR register during 2CTS) is code converted by jamming certain CR
register flip-flops set or reset.
This produces a code of 001111 0
which shifts the monoscope beam to an isolated character at the edge
of the target.
This character, a short underline ( ), marks the pos-
ition of each unused character space on the CRT screen.
4-105
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