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DIDS-402-2AM13
c.
Control Codes - When any control code is shifted into the CE register,
the status of the register flip-flops during CTS+l is (-00----) [this cor-
responds to a character of (00-----) during CTS].
When a control code
is detected in the CE register, a space character is jammed into the
register by NAND-gate decode ASS. 6.
When the operator depresses
the CONTROL key, all control codes circulating in memory appear on
the CRT screen as their lower case equivalent characters.
This is
accomplished by NAND-gate decode ASS. 8 which jams set the two MSB
positions of the CR register.
Since the CONTROL key is normally
depressed for longer than the frame time (16 ms), all control codes
contained in memory are code converted in this manner.
4-23.3 Display Functions
In addition to enabling the generation of visual characters on the CRT screen,
circuits contained on the display logic board enable various edit and cursor
control functions to be performed.
These functions are listed below and described
in the following text:
Step-Right
Step-Left
Advance Line
Cursor Reset
Erase Line
Erase Message
Step-Down
Step-Up
Insert Character
Insert Line
Delete Character
Delete Line
4-23.3. 1 Display Functions Clock
The various operations performed by the display lOgic circuitry are con-
trolled by the special timing circuit shown in figure 4-39.
The output of the
display functions clock, PB3, is connected to the clock input of each edit or
cursor control flip-flop.
The PB3 clock pulse essentially consists of one of the
following:
4-106
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