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DIDS-402-2MlO
Para 3-4/Fig. 3-6
row horizontal lines will appear on the CRT.
When the min9r vertical sweep
voltage is presen t, lines, each approximately one character height in thickness,
will appear on the CRT (figure 3-5E).
3-5 DISPLAY TERMINAL POWER SUPPLIES
High-voltage power supply AS is a compact, solid-state unit which fur-
nishes regulated voltages of +12 kvdc, +500 vdc, and
-1.
2 kvdc .•
Low-voltage power supply A4 is similar in construction to unit AS.
It
furnishes regulated voltages of +22 ydc, -22 vdc, + 100 vdc, and +S vdc.
It
also furnishes two 6. 3-vac outputs.
Optional wiring for 220-volt operation is:
Input
Jumper
3-6
DISPLAY TERMINAL LOGIC
Power Supply
Terminal
11 and 14
12 to l3
To understand more clearly the nature of the display terminal logic,
certain factors of the characters and the cursor should be explained.
Each·
character consists of a special six-bit code in the DIDS-400 System.
All data
transfer in se rial form contains the LSB first.
In the memory circuit, a
cursor slot precedes the six data-bit slots.
The cursor and six bits are cit-
culated through the refresh memory (the cursor is attached to only one charac-
ter in the whole message) as shown in figure
3-6.
The cursor is merely a
place marker in the refresh memory and has no meaning external to the
memory; therefore, only the six data bits are extracted from each memory
word for transmlssion.
Since the computer uses ASCII. which is a seven-bit
code, a conversion from six to seven bits must occur in the storage registers.
A parity bit is added for the purpose,of detecting errors generated in trans-
mlssion.
Since the computer and the DIDS-400 System are asynchronous (not
synchronized by a common timing source), each character must have a start
bit and a stop bit to ensure synchronism.
Two bits are therefore added, one at
the beginning and one at the end of the character, thus yielding 10 bits / character.
The 1200 bits / second are equivalent to 1200 -:- 10. or 120 characters /second.
The logic circuits perform timing, display refresh, display editing functions,
and data transmission to and receipt from the dataphone.
These functions will
be discussed
in~
the following subparagraphs.
r-
ONE CHARACTER TIME
-1
CTS~,---
_ _ _ .....
n . . . . . ___
----,n--___
~n-----
~~_SB
_ _ .. C"
IIsel
~~--"A"--""'~
~~---"T":""----.l.1
MEIIORY~
nJl
n
ru
OATA
..... _ - _ ...
010S67
- ] 0
-.j
~CURSOR
Figure 3
-6.
Memory Data
3-12
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