Tektronix 7623, Instruction Manual

Page: 80 / 266

Circuit Description-7623/R7623 Service
Fig. 3-26. Typical readout display where only channel 1 of the
Right Vertical and Horizontal unit is displayed.
output current on one of ten lines. The outputs of the
Column Decoder stage are identified as C-1 to C-10
(column 1 to 10) which correspond to the column
information encoded by the plug-in unit. Likewise, the
outputs of the Row Decoder stage are identified as R-1 to
R-10 (row 1 to 10) which correspond to the row
information encoded by the plug-in unit. The primary
function of the row and column outputs is to select a
character from the Character Selection Matrix to be
produced by the Character Generator stage. However, these
outputs are also used at other points within the system to
indicate when certain information has been encoded. One
such stage is the Zeros Logic and Memory. During time-slot
1 (TS-1), this stage checks if zero-adding or prefix-shifting
information has been encoded by the plug-in unit and
stores it in memory until time-slots 5, 6, or 8. After storing
this information, it triggers the Display-Skip Generator
stage so there is no display during this time slot (as defined
by Standard Readout Format; see Table 3-2). When
time-slots 5, 6, and 8 occur, the memory is addressed and
any information stored there during time-slot 1 is trans­
ferred out and connected to the input of the Column
Decoder stage to modify the analog data during the
applicable time-slot.
column of the Character Selection Matrix in Fig. 3-25. The
standard format in which information is encoded onto the
output lines is given in Table 3-2 (special purpose plug-in
units may have their own format for readout; these special
formatswill be defined in the manuals for these units).
The encoded column and row data from the plug-in
units is selected by the Column Data Switch and Row Data
Switch stages respectively. These stages take the analog
currents from the six data lines (two channels from each
of the three plug-in compartments) and produce a single
time-multiplexed analog voltage output which contains all
of the column or row information from the plug-ins. The
Column Data Switch and Row Data Switch are sequenced
by the binary Channel Address code from the Channel
Counter.
The time multiplexed output of the Column Data
Switch is monitored by the Display-Skip Generator to
determine if it represents valid information which should be
displayed. Whenever information is not encoded in a
time-slot, the Display-Skip Generator produces an output
level to prevent the Timer stage from producing the control
signals which normally interrupt the CRT display and
present a character.
The analog outputs of the Column Data Switch and Row
Data Switch are connected to the Column Decoder and
Row Decoder stages respectively. These stages sense the
magnitude of the analog voltage input and produce an
Standard Readout Format
TABLE 3-2
Time-Slot Number Description
TS-1 Determines decimal magnitude
(number of zeros displayed or pre­
fix change information) or the
IDENTIFY function (no display
during this time-slot).
TS-2
Indicates normal or inverted input
(no display for normal).
TS-3 Indicates calibrated or uncalibrated
condition of plug-in variable con­
trol (no display for calibrated con­
dition).
TS-4 1-2-5 scaling.
TS-5
Not encoded by plug-in unit. Left
TS-6 blank to allow addition of zeros by
TS-7 Readout System.
TS-8
Defines the prefix which modifies
the units of measurement.
TS-9 Define the units of measurement of
TS-10 the plug-in unit. May be standard
units of measurement (V, A, S,
etc.,) or special units selected from
the Character Selection Matrix.
3-34