Maintenance—492/492P Service Vol. 1 (SN B030000 & up)
Front Panel (refer to diagram 30). Writing to register 74
loads data into shift registers that drive all the lights on the
front panel, including the one for the crt graticule (see Table
4-11). Four 8-bit shift registers store the data, requiring
eight writes of four bits each time (one bit for each register)
to update the front-panel lights. The table below shows the
order that data is entered to control the lights. A 0 turns on
the light (except in the case of the crt graticule); a 1 turns off
the light.
Reading from F4 accesses the keyboard encoder and the
FREQUENCY knob encoder.
Table 4-11
FRONT-PANEL REGISTERS
Write
Number
DB4 DB2
DB1 DBO
Writing data to shift registers for lights (74)
1 MAX
HOLD
ZERO
SPAN
GRAT
ILLUM
CAL
2 CLIP
REMOTE
FINE
LIN
3
AD
DRESSED
10 dB READY NARROW
4 READOUT 20 dB
LINE
TRIG
WIDE
5
AF
IDENTIFY SINGLE
SWEEP
B-SAVE
A
6
EXTR
MIXER
MIN
NOISE
FREE
RUN
VIEW B
7
AUTO
RESOLU
TION
PHASE
LOCK
INT
RUN
VIEW A
8
PULSE
STRETCH
ER
UNCAL EXT
TRIG
SAVE A
A 1 on DB3 initializes encoder (power-up)
Bit Functions
Reading data from switch encoders (F4)
DB7
FREQUENCY down/up (1/0)
DB6—DBO
Switch codes (see Fig. 5-39)
Sweep (refer to diagram 33). The microcomputer writes
to two registers (OF and 1F) to control sweep rate, mode,
hoidoff, interrupts and triggering (see Table 4-12).
Table 4-12
SWEEP REGISTERS
DB7 DB6 DB5 DB4
DB3
Time/Div
Sweep Rate and Mode (OF)
1
1
0
1 1
20 μΞ
1
0
1 1 1
50 μβ
1
0 0
1 1
100 μΞ
0 1
0
1 1
200 ^s
0 0 1 1 1
500 με
0
0 0
1 1
1 ms
1
1
0
0 1
2 ms
1
0 1 0
1 5 ms
1
0 0 0
1
10 ms
0
1
0 0
1
20 ms
0 0 1 0
1
50 ms
0 0 0 0
1
100 ms
1 1
0 0
0
200 ms
1
0
1
0
0
500 ms
1
0 0
0 0
1 s
0 1 0 0 0
2s
0
0
1 0 0
5 s
0 0 0 0 0
10 s
1 1 1 1 1
Manual
0 1 1 1
1 External
A 1 on DB2 sets single-sweep mode
A 1 on DBO sets trigger in single-sweep mode
Bit
Function
Hoidoff, Interrupt, Trigger (1F)
DB7 1 enables end-of-sweep interrupt
DBS
DB5
Sweep Hoidoff
0 0
Short
0 1 Medium
1
0
Long
DB4 DB3
Trigger Mode
0 0 Free run
0 1
Internal
1
0
External
1
1
Line
DBO
Aborts sweep
4-48
REV SEP 1983
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