Theory of Operation—2246 1Y and 2246 Mod A Service
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
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 colum n, 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
Readout Type
U2414-3
U2414-13
Stationary Text
0.6 V
U2412 output
Horizontal Ref Cursor
REF CURSOR
U2412 output
Horizontal Delta Cursor
DELTA CURSOR
U2412 output
Vertical Ref Cursor
0.6 V
U2413 output
Vertical Delta Cursor
0.6 V
U2413 output
Table 3-30
Possible Signal Conditions to U2416
Readout Type
U2415-3
U2415-13
Stationary Text
2.0 V
U2413 output
Horizontal Ref Cursor
2.0 V
U2413 output
Horizontal Delta Cursor
2.0 V
U2413 output
Vertical Ref Cursor
REF CURSOR
0 mA
Vertical Delta Cursor
DELTA CURSOR
0 mA
REV OCT 1991
3-51
Summary of Contents for 2246 1Y
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