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DIDS-402 -2AM13
attached. The remaining characters, however, can accept the cursor; this is the
main purpose of cursor control operations .•• to remove the cursor from one
character and attach it to another.
The following text briefly describes the function of each portion of the
editing and cursor control logic (see figure 4-17).
4-17. 1 Individual Function Flip-Flops
The individual flip-flops used to accomplish the various operations are
normally operated independently, but in some cases are connected to other
function flip-flops.
An example of this is the relationship between the step-right
and advance-line flip-flops where the step-right operation causes an advance
line if it occurs at the end of a line.
To initiate an operation, signals are coupled from either the keyboard
assembly or control code decodes connected to buffer register D3.
When any key-
board keys are depres sed, a high-to-Iow going level is developed; this level is
coupled to both the flip-flop associated with the key and the sample strobe circuit.
The sample strobe pulse developed by this circuit is used to clock the keyboard
signal into the appropriate flip-flop.
4-17.2 Sample Strobe Circuit
The sample strobe circuit consists of two interconnected flip-flops (A2l. 2
and A2l. 8) which are used to prevent the repetition of an operation when the
function key is held depressed.
To accomplish this, only the first frame pulse
after the key depre ssion is permitted to clock the individual function flip-flop.
This frame pulse then becomes the sample strobe pulse and is used to clock the
appropriate flip-flop.
To repeat the function, the key must be released and
depressed again or the CYCLE key must be depressed.
When the CYCLE key
is held depressed in conjunction with any function key, the function is repeated
by a sample strobe which reoccurs at
6
Hz.
The second detent position of the
. . (step right) and ... (step left) function keys operates in a similar manner to
repeat the function at a 12-Hz rate.
The function-complete circuit consists of flip-flop A40. 8 and as sociated
OR- gate A2. 8.
The purpose of the function-complete flip-flop is to re set the
individual function flip-flop on the trailing edge of the cursor at the completion
of an operation.
Exceptions to this rule are the step-up, insert, and delete-
function flip-flops which are re set by other circuits.
4 -17. 3 Input and Output Display Logic
The input and output display logic consists of series-connected OR-gates at
both the input and output of the delay-line electronics.
The input display logic consists of OR gates A3. 8 and A4. 8.
Depending
upon the operation initiated, data is inhibited, altered, or permitted to pass
unchanged as
it
leaves the character entry register and passed through the
OR-gates to the delay-line electronics.
4-41
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