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DIDS-402 -2AM13
The step-right function is performed each time one of the following occurs:
a.
The step-right ( - ) key is depressed
b.
A horizontal tab (HT) control code is received from the CPU without
being preceded by an ESC code
c.
Any key capable of producing a digital code is depressed and data
is entered into memory (INTERLK)
d.
A character is read into or out of memory by SDL (CRQ)
To perform a step-right function, the cursor is located in memory by
sensing its presence in the cursor-located flip-flop of the CE register.
When
. the cursor is found, it is erased and then reinserted into memory at the entrance
to the CE register.
The combined effect of these two operations is to delay the
cursor by one character time.
The step-right function is described below.
When the step-right ( - ) key or any key capable of producing a digital code
is depre ssed, the input to step-right flip-flop A32. 9 goes high.
PB3, which
occurs from 0 to 16 ms later, sets A32. 9 high to enable one input to NAND-gates
A39.8 and A45. 8.
When the cursor appears in the CE register and is not
attached to the last character of the line, NAND-gate A39. 8 is enabled.
The
output of A39. 8 (a low) is applied to A4. 8 of the input display logic which places
a low at the entrance to the delay line.
Since this low is in coincidence with the
cursor, the cursor is erased.
Simultaneously, a high is applied to the entrance
of the CE register and the reset input of the function complete flip-flop.
During
2CTS, this high is clocked into the MSB flip-flop of the CE register as the cursor
and the function complete flip-flop is clocked to reset.
During the following
phase time (3CTS+l), Function Complete jams A32. 9 reset to disable the function.
If the cursor is attached to the last character of the line, a step-right
function automatically advances the cursor to the first character position of the
next line.
LWL, which appears in coincidence with the cursor,
inhibits
NAND-gate A39. 8 and enables NAND-gate A45. 8.
This sets the advance-
line flip-flop and causes an advance-line function (paragraph 4-23.3.4) to be
accomplished.
As shown in figure 4-40, the step-right function is also performed each
time an HT code is received from the CPU (HT) or each time a character is
shifted into or out of the delay line by SDL (CRQ). However, since these are
jam inputs, the step-right function,is performed without the use of the PB3
clock pulse.
4-23.3.3 Step-Left Function
The step-left cursor control function moves the cursor one character
position to the left.
The visible effect of step left is to move the cursor one
character position closer to the left of the CRT screen.
In memory, step left
advances the cursor by one character time, causing it to appear in the CE regis-
ter 13 fJ.s earlier than it had prior to the step.Jeft function (see figure 4-41).
4-110
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