Table of Contents
Advertisement
A9. 12 - CTS
A15.12
A15.9
Al0.12
A9.S
AI4.S
A9.6
AS.a
DIDS 68-658
DIDS -402 -2AM 13
I
...
~~-------
EIGHT CHARACTER TIMES
--------~~
I
I
I
I
~
I--
ONE CHARACTER TIME
i
111.....-......In
n
n
n
n ....
_~n
.... _.,Jn ..... ----'nL-_1l..-
'L.. ____
...I
I~----------------~
I
u
____________________________________ -...InL.. ____________ _
CTS OF STH CHAR
__________________________________
~n~
___________________
CTSOFnHCHAR
Figure 4-59.
Eight-Character Counter, Tim.ing Diagram.
4-24.6 Character Counter
The character counter (figure 4-60) counts the num.ber of characters con-
tained on a horizontal line.
The character counter decodes two general outputs.
NAND-gate AB. 3 produces an output pulse eight characters wide (104 !Jos) which
is used to designate line character counts Bl through BB.
AND-gate A2. B pro-
duces an output pulse which is also eight characters wide; this pulse is high
during line character count 73 through BO.
Timing pulses developed by the eight-
character counter and character counter decodes are described in the following
text (see figures 4-60 and 4-61).
Before examining the various timing outputs, an im.portant factor con-
cerning visual character generation should be noted.
It takes one character time
(13 !Jos) to shift a complete character out of memory and into the CE register.
At the end of this 13 !Jos, the character code is transferred into the CR register
during 2CTS.
During the following 3(CTS+1) through 2(CTS+1), the video ampli-
fier is cut off by a blanking pulse (simultaneously, another character is being
shifted into the CE register).
Beginning with the trailing edge of 2(CTS+l), a
sawtooth voltage developed in the m.onoscope deflection amplifier begins moving
the monoscope beam across the character symbol to produce a video output.
This scan across the character takes an additional 13 !Jos.
Thus, from the time
the character enters the CE register, l3!Jos elapse before the character is
displayed on the screen.
This one-character-time delay is reflected in the
timing circuit outputs.
For example, LWL occurs during CTS of character count 79.
This pulse
signifies that the last displayable character is held in the CE register.
At CTS
of characte r count BO, the last displayable character is displayed on the screen
and the first retrace character is held in the CE register.
Thus, at the same
time the Display Terminal enter s horizontal retrace, a horizontal retrace charac-
ter is transferred into the CR register.
4-141
Advertisement
Chapters
Table of Contents
