Tektronix 7623, Инструкция по эксплуатации

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Circuit Description— 7623/R7623 Service
timing sequence began. However, character-generation does
not start until the readout intensity level has been
established. The triangular Character Scan ramp runs
negatively from about —2 volts to about —8.5 volts and
then returns back to the original level. This waveform
provides the scanning signal for the Character Generator
stages (see diagram 10). The Full Character Scan adjust­
ment R2128 sets the DC level of the Character Scan ramp
to provide complete characters on the display.
The Timer stage operates in one of two modes as
controlled by the Display-Skip level at pin 4. The basic
mode just described is a condition which does not occur
unless all ten characters of each word (60 characters total)
are displayed on the CRT. Under typical conditions only a
few characters are displayed in each word. The Display-Skip
level at pin 4 determines the period of the Timer output
signal. When a character is to be generated, pin 4 is LO and
the circuit operates as just described. However, when a
character is not to be displayed, a HI level is applied to pin
4 of U2126 through CR2125 from the Display-Skip
Generator stage. This signal causes the Timer to shorten its
period of operation to about 210 microseconds. The
waveforms shown in Fig. 3-30 show the operation of the
Timer stage when the Display-Skip condition occurs for all
positions in a word. Notice that there is no output at pin
12, 13, 14, and 16 under this condition. This means that
the CRT display is not interrupted to display characters.
Also notice that the triangle waveform at pin 6 does not go
as far negative and that the negative portion of the
trapezoidal waveform at pin 10 is shorter. Complete details
on operation of the Display-Skip Generator are given later.
The Single-Shot Lockout level at pin 2 determines the
operating mode of U2126. If this level is LO, the Timer
operates as just described. However, if the Single-Shot
Lockout stage sets a HI level at this pin, the Timer stage is
locked out and can not produce any output signals (see
Single-Shot Lockout description for further information).
The READOUT intensity control R2124 sets the inten­
sity of the readout display independently of the INTEN­
SITY control. The READOUT intensity control also
provides a means of turning the Readout System off when a
readout
display is not desired. When R2124 is turned fully
counterclockwise, switch S102 opens. The current to pin
11 of U2126 is interrupted and at the same time a positive
voltage is applied to pin 4 through R2122 and CR2124.
This positive voltage switches the stage to the same
conditions as were present under the Display-Skip con­
dition. Therefore, the CRT display is not interrupted to
present characters. However, time slot pulse continue to be
generated.
Fig. 3-30. Timer stage operation when Display-Skip condition
occurs.
3-38