Tektronix 492 - Page 159

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Maintenance—492/492P Service Vol. 1 (SN B030000 & up)
Log and Video Amplifier (refer to diagram 22). Two
registers receive data from the microcomputer (see Table
4-6); one controls video offset (78) and the other controls
display modes and vertical scale factor (79).
Table 4-6
LOG & VIDEO AMP REGISTERS (78 AND 79)
Bit
Function/Mode
Digital Storage (refer to diagram 24). Two registers (at
7A and FA) on the Vertical Digital Storage board transfer
display data to and from the microcomputer for 492P GPIB
operations. Another register (at 7B) controls digital storage
functions (see Table 4-8).
Table 4-8
DIGITAL STORAGE REGISTERS (7A, FA, AND 7B)
Video Offset (78)
DB7—DBO
Video offset, LSB = 1/4 dB, total
range = 63.75 dB
Modes and Scale Factor (79)
DB7
Pulse stretcher on/off (1/0)
DB6
Identify offset on/off (1/0)
DB5
0
DB4
1 Lin
1 0 Log
0
0 Full-screen deflection
DB3—DBO Log vertical scale factor in dB/div
Video Processor (refer to diagram 23). A register (7C)
controls out-of-band clamping, video filtering, and leveling
(see Table 4-7).
Table 4-7
VIDEO PROCESSOR CONTROL (7C)
Bit
Function
DB5 DB6
DB7 Out-of-Band Clamp
1 1
0
No clamp
1
0 0
Clamp upper 5 div
1 1 1 Clamp lower div
0
1
0
Clamp lower 5 div
DB4
DB3
DB2 DB1 Video Filter
0 0 0 0
Off
0
0 0
1
30 kHz
1
0 0
1
3 kHz
1
1
0
1
300 Hz
0
0
1 1
30 Hz
1
0
1 1
3 Hz
1
1 1 1 0.3 Hz
DBO
Base-line Leveling
on/off (1/0)
Bit
Function
Digital Storage Input (7A)
DB7—DBO Data values for digital storage. A write to
7B clears the address counter so values
are stored for points on display starting at
left and proceeding to right in order.
Digital Storage Output (FA)
DB7—DBO Data values from digital storage. A write
to 7B initializes output to begin at left of
trace and proceed to right.
Digital Storage Control (7B)
DB7 Halt/run (0/1) storage acquisition
DB6 DB5 PEAK/AVERAGE cursor
1
1
Knob position
1 0 PEAK
0
1
AVERAGE
DB4 MAX HOLD on/off (1/0)
DB3
VIEW B -A on/off (1/0)
DB2 VIEW B on/off (1/0)
DB1
VIEW A on/off (1/0)
DBO SAVE A on/off (1/0)
4-46
REVJUN 1983