Timer; Time-Slot Counter - Tektronix 7140 Instruction Manual

The Word Trigger stage produces a trigger from the End-of- The Timer stage operates in one of two modes as controlled
Word pulse generated by the Time-Slot Counter stage after by the Display-Skip level at pin 4. The basic mode just de-
the tenth time-slot. This Word Trigger pulse advances the scribed is a condition that does not occur unless all ten char-
Channel Counter to display the information from the next
acters of each word (80 characters total) are displayed on
channel or plug-in. This Word Trigger stage can also be ad-
the CRT. Under typical conditions, only a few characters are
vanced to jump a complete word, or a portion of a word,
displayed in each word . The Display-Skip level at pin 4 de-
when a Jump Command is received from the Row Data
termines the period of the Timer output signal . When a char
Switch stage.
acter 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 02126 through
TIMER
CR2125 from the Display-Skip Generator stage. This signal
causes the Timer to shorten its period of operation to about
The Timer stage produces the timing sequence for all cir-
210 microseconds . The waveforms in Figure 3-13 show the
cults within the Readout System . This stage produces six
operation of the Timer stage when the Display-Skip condi-
time-related output waveforms (see Fig. 3-11). The triangle
tion occurs for all positions in a word . Notice that there is no
waveform produced at pin 6 forms the basis for the remain-
output at pins 12, 13, and 14 under this condition. This
ing signals. The basic period of this triangle waveform is
means that the CRT display is not interrupted to display
about 250 microseconds, as controlled by RC network
characters . Also notice that the triangle waveform at pin 6
R2135 and C2135. The triangle waveform is clipped and
does not go as far negative, and that the negative portion of
amplified by 02126 to form the trapezoidal output signal at
the trapezoidal waveform at pin 10 is shorter. Complete de-
pin 10 . The amplitude of this output signal is exactly 15
tails on operation of -the Display-Skip Generator are given
volts, as determined by 02126 (exact amplitude is neces-
later.
sary to accurately encode data in plug-in units; see Encod-
ing the Data). The trigger output at pin 5 provides the
The Timer operation is also controlled by the Single-Shot
switching signal for the Time-Slot Counter and Word Trigger
Lockout level at pin 2. If this level is LO, the Timer operates
stages .
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-
The signals at pin 12, 13, and 14 are produced only when Shot Lockout description for further information) .
the triangle waveform is on its negative slope and the trape-
zoidal waveform has reached the lower level. The timing
A negative voltage on the readout intensity line sets the
sequence of these waveforms is important to the operation
intensity of the readout display independently of the A or B
of the Readout System (see expanded waveforms in Fig. 3-
INTENSITY controls . The Readout Intensity line also pro-
12) . The Z-Axis inhibit command at pin 14 is produced first.
vides a means of turning the Readout System off when a
This negative-going signal provides a blanking pulse to the
readout display is not desired. When the Readout Intensity
Z-Axis Logic stage to blank the CRT before the display is
line is left open, the current from pin 11 of 02126 is inter-
switched to the Readout System . It also produces the
rupted, and at the same time, a positive voltage is applied to
strobe pulse through 02138 and CR2139 which is con-
pin 4 through CR2124 . The positive voltage switches the
nected to pin 15 of 02232.
stage to the same conditions as were present under the
Display-Skip condition . Therefore, the CRT display is not
The purpose of this configuration is to prevent the Zeros
interrupted to present characters . However, time-slot pulses
Logic and Memory stage 02232 from storing incorrect data
continue to be generated.
during the quiescent period of the strobe pulse. When the
strobe pulse goes positive, CR2139 is reverse biased to dis-
TIME-SLOT COUNTER
connect 02138 and allow 02232 to operate in the normal
manner .
Time-Slot Counter 02159 is a sequential switch which di-
rects the trapezoidal waveform input at pin 8 to one of its 10
output lines. These time-slot pulses are used to interrogate
The next signal to be produced is the X-Y Inhibit Command
the plug-in units to obtain data for the Readout System . The
at pin 13 . This positive-going signal disconnects the plug-in
trigger pulse at pin 15 switches the Time-Slot Counter to the
signals from the vertical and horizontal deflection systems.
next output line, causing the output signal to be sequenced
The Ready signal is also derived from this output and con-
consecutively from time-slot 1 through time-slot 10 . Figure
nected to the Character Generator stage and the two Out-
3-14 shows the time relationship of the time-slot pulses . No
put Amplifier stages .
tice that only one line carries a time-slot pulse at any given
time . When time-slot 10 is completed, a negative-going end-
The Z Readout output at pin 12 is produced next . This cur-
of-word pulse is produced at pin 2. The end-of-word pulse
rent is connected to the CRT circuit to unblank the CRT to
provides a drive pulse for the Word Trigger stage and also
the intensity level determined by the voltage on the Readout
provides an enabling level to the Display-Skip Generator
Intensity line .
during time-slot 1 only .
REV NOV 1985
Theory of Operation-7104
3- 43