Tektronix 5441 Instruction Manual page 50

Theory of Operation-5441lR5441
, 1 1 1 1 1 1 1 1 1 1
Time-slot
pulse 1 O V
Pin 3
Time-slot O V
pulse 2
Pin 13
The amplitude of the time-slot pulses is exactly -15 V
as determined by the timer stage. Therefore, the resultant
output from the plug-in units can be accurately controlled by
the programming resistors in the plug-in units.
Figure 3-9(A) shows an idealized current waveform of
row analog data, which results from the 10 time-slot pulses.
Each of the steps to current shown in these waveforms cor-
respond to 100 pA of current. The row numbers on the left-
hand side of the waveform correspond to the rows in the
character selection matrix shown in Fig. 3-8. The row ana-
log data is connected back to the readout system via con-
tact 828 of the plug-in interface. Idealized column current
waveforms at contact A28 of the plug-in interface are
shown in Fig. 3-9(B).
Time-slot
pulse 3
Referring to the character selection matrix, two units of
Pin 12 column current, along with the two units of row current en-
coded during TS-1, indicates that two zeros should be add-
ed to the display. One unit of column current during time-slot
2, along with the one unit of current from the row output,
instructs the readout system to add an invert arrow to the
display.
No column current output during TS-3 means no display
on the crt (see Display-Skip Generator for further informa-
tion). Two units of column current are encoded during TS-4.
~ h e i e is no row current encoded during this time-slot; this
Fig. 3-7. Time relationship of the time-slot (TS) pulses produced
results in the numeral being displayed on the crt. Neither
by
U1025.
row nor column analoa data is encoded durina time-slots 5.
6, and 7. During TS-&two units of column current and three
units of row current are encoded. This addresses the
p
pre-
Word Counter
fix in the character selection matrix. The final data output is
The word counter, made up of three flip-flops in integrat-
provided from time slot 9; three units of column current and
ed circuit U1075, is a binary counter that produces the word
units
current cause a
be
address code for the column and row decoder stages.
The resultant crt readout is 100 pV.
This code instructs these stages to sequentially select
and display the data from the plug-ins. The input channel
that is displayed with each combination of the word address
code is given in the discussion for the applicable stages.
Encoding The Data
Data is conveyed from the plug-in units to the readout
system in the form of an analog code having up to 11 cur-
rent levels (from 0 to l mA in 100 pA steps). The characters
that can be selected by the encoded data are shown on the
character selection matrix (see Fig. 3-8). Each character re-
quires two currents to define it; these currents are identified
as the column current and the row current, which corre-
spond to the column and row of the matrix. The column and
row data is encoded by resistive programming in the plug-in
units. The resistors are connected between the time-slot
lines and the row or column lines.
The column analog data encoded by the plug-in unit can
be modified by attenuator probes connected to the input
connectors of vertical plug-in units. A special coding ring
around the input connector of the plug-in unit senses the
attenuation ratio of the probe (with readout-coded probes
only). The probe contains a resistor that causes additional
column current. For example, if a 10X attenuator probe is
connected to a plug-in with the coding for 100 pV, an addi-
tional unit of current is added to the column analog data
during time-slot 1. Since two units of current were encoded
in Fig. 3-9, this additional current results in a total of three
units of column analog current during this time-slot.
Referring to the character selection matrix, three units of
column current, along with the two units of row current,
indicates that the prefix should be reduced. Since this in-
struction occurs in the same time-slot that previously indi-
cated that two zeros should be added to the display, and
3-14
REV MAY 1982