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DIDS-402-2AM13
h.
ETX -
The ETX character terminates both the message and the
display terminal receive mode.
As soon as ETX is received and
decoded, the Display Terminal begins transmitting data from the
cursor position to the previously inserted ETX code.
SECTION II
FUNCTIONAL DESCRIPTION
4-13 GENERAL DESCRIPTION OF SECTION CONTENTS
This section contains information concerning the operation of the Display
Terminal on a block diagram basis.
Functionally, the Display Terminal can be
divided into several major circuits which work in conjunction to perform specific
internal functions.
These circuits are grouped and described in detail with
respect to purpose and functional operation.
Control codes and control keys are
discussed on a comparative basis in order to provide a greater understanding
of their purpose and relationship.
4-14 OVERALL BLOCK DIAGRAM
The overall block diagram of the Display Term.ina1 is shown in figure 4-12.
The Display Terminal is functionally divided into the following circuits:
Character generation and refresh
Buffer register and interface
Editing and cursor control logic
Timing
Raster Generation
Powe r supplie s
4-15 CHARACTER GENERATION AND REFRESH
An important aspect of display terminal operation is the manner in which
visual characters are developed for display on the CRT screen.
While the
operation of these circuits is not difficult to understand, a thorough knowledge of
the principles involved is necessary to understand the various editing and cursor
control functions.
The character generation circuits consist of two interrelated parts: the
keyboard-monoscope circuits and the refresh-memory loop.
The keyboard mono-
scope circuits convert the mechanical depression of a specific character key into
a corresponding visual character on the CRT screen.
The refresh-memory loop
periodically refreshes the displayed character so that a flicker-free presentation
remains on the screen until the message is erased.
4-18
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