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DIDS-402-2MIO
Para 3-6. 3/Fig. 3-13
To erase the message, a logical 0 is inserted into each bit slot to the right
of the cursor bit.
The frame pulse terminates this funCtion and the line is erased
in a similar manner.
However, the last word of the line pulse terminates the
function (figure 3-13).
In order to advance the cursor to the next line, the cursor
must be delayed in time until the first character slot of the next line occurs.
To
accomplish this, the cursor is removed from its slot and inserted in the cursor
slot of the first word of the next line when it reaches the input to the shift register
(figure 3-14).
This function is terminated with the A.plllse.
To move the cursor
to the first character slot of the previous line, the curSor must be advanced in
time by the frame period minus one horizontal line time and the time remaining
on the cursor line.
This function is controlled by a counter which counts the
nurnberof active horizontal lines minus two (figure 3 -15).
The insert function is accomplished with the aid of a second seven-bit shift
register.
To insert a character, all characters to the right of the curBor and on
the same line as the cursor are delayed in .time by one character period.
The
second shift register, which has the code of 0000000 stored, is allowed to become
a part of the memory loop when the cursor is located in the first shift register.
G---------,
KEYBOARD
S
ERASE
I
-::::
I
I
I
I
I
I
I
F~
KEYBOARD
Co
MESSAGE
R
FF
S ERASE
-
R
LINE
FF
DISPLAY LOGIC
,Q
I
I
I
I
..J
I
~
2:
It:
I
0
z
I
I
L ________ .
_-.J
010567-9
SHIFT
..
REGISTER
DELAY LINE
,I
Figure 3-13.
Display Editing Erase Mode
•
DISPLAV
LOGIC
This inserts a new character of all 0
I
S
in the memory loop.
The second shift
register is removed from the memory loop when it contains the last word of the
line.
Therefore, the character that was in the last active slot of the line is re-
moved :from the memory loop (figure 3 -16).
3-20
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