Timer - Tektronix 7623A Instruction Manual

Theory of Operation—7623A/R7623A Service
running mode, so the waveform display is interrupted randomly to display characters. However, under cer-
tain conditions (such as single-shot photography), it is desirable that the Readout System operate ina
triggered mode where the readout portion of the display is normally blanked out, but can be presented on
command. The Readout Mode switch, $2110, determines the operating mode of the Readout System.
TIMER
Timer U2126 establishes the timing sequencefor all circuits within the Readout System. This stage
produces seven time-related output waveforms {see Figure 3-28). The triangle waveform produced at pin 6
forms the basis for the remaining signals. The basic period of this triangle waveform is about 250 micro-
seconds as controlled by RC network R2135-C2135. The triangle waveform is clipped and amplified by
U2126 to form the trapezoidal output signal at pin 10. The amplitude of this output signal is exactly 15
volts as determined by U2126 (exact amplitude necessary to accurately encode data in plug-in units; see
Encoding the Data). The Trigger output at pin 5 pro-
vides the switching signal for the Time-Slot Counter . yp pe \ pos poe
_ Vv
and Word Trigger stages. ' f ' FOS) | of OV
CHARACTER !
SCAN eref e s ccend Y.. ee npeeefe edu.
PIN 16 oy
The signals at pins 12, 13, 14, and 16 are pro- / em press opt cope
duced only when the triangle waveform has reached eno vaso PAPER ERT RESET ECE PEE
the lower level. The timing sequence of these wave- _. a
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forms is important to the operation of the Readout Joo ee p o cenk web | OS) | |
System (see expanded waveforms in Figure 3-29). iZAXIS _ i. fof Et
The Z-Axis Inhibit at pin 14 is producedfirst. | 4.
This negative-going signal provides a blanking pulse pendent veafeeay PTH 4 reeefererteees fe eee OV
to the Z-Axis Logic stage (see diagram 2) to blank
the crt before the display is switched to the Read-
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| |
out System. It also produces the Strobe pulse through X-Y¥ . |
. a. INHIBIT Oe ' fm 3
Q2138 and CR2142 to signal other stages within the | | 1 j0V
Readout System to begin the sequence necessary to coef wfc hutdibulensdoccce
produce a character. The collector level of 02138 is | '
also connected to Character Generator No. 2, U2272, preety my
acti
|
soy
poasl
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through CR2140. This activates U2272 during the | ~ | | ,
i i | ~ 4
quiescent period of the Strobe pulse (collector of Z READOUT | , | | re 78 Vv
Q2138 negative) and diverts the output current of pope "yy L | |
Row Decoder U2185 to row 2. The purpose of this PE EE ET PET EEE
. . . NOTE: TEST OSCILLOSCOPE EXTERNALLY TRIGGERE
configuration is to prevent the Zeros Logic and FROM TP2251
Memory stage U2232 from storing incorrect data
during the quiescent period of the Strobe pulse. Figure 3-29. Detail of output at pins 12, 13, 14, and 16
When the Strobe pulse goes positive, CR2140 is re- of U2126.
verse-biased to disconnect Q2138 from U2272 and allow the Row Decoder to operate in the normal manner.
The next signal to be produced is the X-Y Inhibit at pin 13. This positive going signal
disconnects the plug-in signats from the vertical and horizontal deflection systems...
3-51