Trigger Selection Logic - Tektronix 2246 1Y Service Manual

hysteresis is increased so that a larger signal
change is required to produce a state change at the
output of the comparators. Trigger Coupling control
logic is shown in Table 3-6.
Another signal source selectable in the Trigger
Coupling Selectors is the output of the TV Trigger
Detector (TV LINE or TV FIELD). An applied com ­
posite video signal is separated so that the hori­
zontal line or vertical field sync pulse can be used to
Front Panel
Coupling
Selection
SLOPE
A Sweep Mode (U421) AUTO LEVEL, AUTO, NORM, or SGL SEQ
DC
NOISE REJ
HF REJ
LF REJ
AC
DC
NOISE REJ
HF REJ
LF REJ
AC
B Sweep Mode (U431) AUTO LEVEL, RUNS AFTER or NORM
DC
NOISE REJ
HF REJ
LF REJ
AC
DC
NOISE REJ
HF REJ
LF REJ
AC
Table 3-6

Trigger Selection Logic

Latched Bit Values
TS2
0 0
1 0
0 1
0 0
0 1
A Sweep Mode (U421) TV LINE or TV FIELD
1
0
1 0
1
0
1
0
1
0
0 0
1
0
0 1
0 0
1
0
B Sweep Mode (U432) TV LINE
1
0
1
0
1
0
1 0
1 0
Theory of Operation—2246 1Y and 2246 Mod A Service
trigger the oscilloscope for Television signal display
(see TV Trigger Detector description). Selection
between LINE or FIELD for the A Trigger source is
done by multiplexer U1104A with its output being
applied to pin 18 of U421B. Pin 18 of U431B in the B
Trigger system has an input of either the TV Line
sync signal, for TV triggering of the B Sweep, or the
output of the Measurement Signal Low-Pass Filter,
when the DC measurement mode is active.
TS1 TSO
1 0
1 0
0 1
1 1
0 0
0 0
0 0
0 0
0 0
0 0
1
0
1
0
1
0
1 1
0 0
0 0
0 0
0 0
0 0
0 0
Description
DC Coupled
DC Coupled, Noise Reject
HF Reject
LF Reject
AC Coupled
TV Input, Noise Reject
TV Input, Noise Reject
TV Input, Noise Reject
TV Input, Noise Reject
TV Input, Noise Reject
DC Coupled
DC Coupled, Noise Reject
HF Reject
LF Reject
AC Coupled
TV Input, Noise Reject
TV Input, Noise Reject
TV Input, Noise Reject
TV Input, Noise Reject
TV Input, Noise Reject
3-13