Raytheon DIDS-400 Series Technical Manual page 173

DIDS-402-2AMl3
a. Set step-up flip-flop (Al4. 5 goes low and stays low)
b. Locate cursor
c. Erase cursor, enable 88-count, enable l2-count
d. 88-count complete
e. Insert cursor
f • Locate cur sor
g. Erase cursor, enable 88-count.
h. 88 -count complete
i. Insert cursor
t.
Repeat
f-,
g, h, and i until 12 -count is complete
The circuit continues in this manner until a 12 count is decoded by NAND-
gate A59.6 (see figure 4-46). This level is applied to Al4. 5 and returns A14. 5
to its quiescent "state (A14.5 = HIGH). Thus, 12 lines have been counted by
clocking the l2-count circuit with A pulses. Since A appears at the first charac-
ter of line position, the 88-count complete is enabled from 0 to 1.144 ms later,
depending upon the character slot location of the cursor when the function was ini-
tiated. When the 88-count cqmplete pulse arrives from the
88-count_~ipple
counter,
A15.6 is again enabled to insert the cursor. Simultaneously, the function-com-
plete flip- flop is enabled, but this time the function complete pulse has no
effect because of the inhibited status of A 7.11 (A14.6 is low). T'hus, prior to
locating the cursor in the CE register, A14.8 is still low and a high is applied
to AlS. 3 and to the 88-count enable-reset flip-flop AS. 9. On the rising edge of
the
curso~,
the 13th consecutive 88 count is enabled, the cursor is erased, and
A14.8 returns to its quiescent state. The, function is complete as soon as the
88-count complete pulse enables A15. 6 for the 13th time to insert the cursor.
The cur sor has now been
I
stepped up
I
by actually stepping it down for 12 line
counts and 13 - 88 counts. .
4-23.3. 12 Insert Character Function
The insert-character edit function replaces the character associated with
the cursor with an Idle character (all lIs) and moves all other characters on the
line to the right by one character position. In memory, insert character consists
of replacing the cursor character with a previously stored Idle character. This·
Idle character is code converted in the CR register and appears as a short
underline (,) on the CRT screen. As previously stated, this symbol is used to .
indicate a blank space in memory which can be used to insert a usable character.
Simultaneously, all characters between the cursor and the end of the line are
delayed by 13 J.LS due to insertion of an lextra' 8-bit register into the memory loop.
Thus, at the end of the line, the last character of the line is delayed sufficiently
to place it into horizontal retrace. Since characters cannot be displayed once
they enter the retrace area, the last character of the line (which is held in the
extra re giste
r)
is dropped (see figure 4- 51).
4-131