Switch Board And Interface (Diagram 10); Display Possibilities; Possible Signal Conditions - Tektronix 2246 1Y Service Manual

The voltage at U2416 pin 14 depends on two things:
the current from U2414 pin 13, and the voltage at
U2414 pin 3. The possible displays are given in Table
3-29.
The voltage at U2416 pin 8 depends on two things:
the current from U2415 pin 13, and the voltage at
U2415 pin 3. The possible conditions are shown in
Table 3-30.
SWITCH BOARD AND INTERFACE
(Diagram 10)
The front-panel LEDs that backlight the switches and
panel labels are schematically arranged in a matrix of
eight rows and six columns. The front-panel switches
are arranged in a matrix of 16 rows and six columns.
Each LED and switch is connected to a distinct row/
column intersection, with a column of LEDs and a col­
umn of switches being common and enabled by the
same signal.
At intervals of about 2 ms, a column of LEDs is
refreshed (turned on or off) and the status (open or
Readout Type
Stationary Text
Horizontal Ref Cursor
Horizontal Delta Cursor
Vertical Ref Cursor
Vertical Delta Cursor
Readout Type
Stationary Text
Horizontal Ref Cursor
Horizontal Delta Cursor
Vertical Ref Cursor
Vertical Delta Cursor
REV OCT 1991
Theory of Operation—2246 1Y and 2246 Mod A Service
closed) of the connected column of switches is read.
All six columns of LEDs and the six columns of
switches are completely refreshed and checked
every 12 ms. The timing is fast enough to prevent
flicker of the LEDs and to catch a push button
closure.
LED Refresh
Assume LED column ASO is being refreshed. First,
the LED Cathode Register, U2524, is loaded with a
data byte from the Measurement Processor. That
byte defines the LEDs that are on for that column, and
the outputs of Cathode Driver U2525 for the " on"
LEDs are low. Then, a high on the DO bit of the Meas­
urement Processor Data Bus is latched into LED An­
ode Register U2523 with the LED ANODE CLK signal.
That high turns on the associated Darlington transis­
tor (Q2506 for the ASO colum n), and the LEDs in that
column that also have their cathodes low from U2525
are turned on.
Table 3-29

Display Possibilities

U2414-3
0.6 V
REF CURSOR
DELTA CURSOR
0.6 V
0.6 V
Table 3-30
Possible Signal Conditions to U2416
U2415-3
2.0 V
2.0 V
2.0 V
REF CURSOR
DELTA CURSOR
U2414-13
U2412 output
U2412 output
U2412 output
U2413 output
U2413 output
U2415-13
U2413 output
U2413 output
U2413 output
0 mA
0 mA
3-51