Trigger Source Select; Vertical Mode Select; Horizontal Mode Select - Tektronix 2246 1Y Service Manual

mode is enabled, the force B1/B2 feature is
disabled, and THO is strobed once (or RESET
is strobed once while THO is high). At this
point, output pins ATS2, ATS1, ATSO, and A
SLOPE are set to AC3, AC2, AC1, and ACO
respectively; and output pins BTS2, BTS1,
BTSO, and B SLOPE are set to BC3, BC2,
BC1, and BOO respectively. The Measure­
ment Processor then strobes the latches in
the Trigger Coupling Select Logic circuits to
make the trigger coupling selections. The
RAM load mode is then disabled to resume
normal Display Sequencer operation.
AS2, AS1, ASO: A Trigger SOURCE select
bits. See Table 3-11 for the bit encoding of
the control signals when not loading the RAM
or coupling circuits.
Table 3-11

Trigger Source Select

AS2 AS1
ASO
0 0
0
1
0 0
0 1 0
1 1
0
1
0 0
1 0 1
1 1
0
1 1 1
For any binary code except 111; AS2, AS1,
and ASO are presented on output pins ATS2,
ATS1, and ATSO respectively after a THO
rising edge. For binary code 111, the data on
the three output pins will correspond to the
channel being enabled
alternates as the channel displays alternate
and change state on the rising edges of THO.
The RAM load mode is disabled to get the A
Trigger SOURCE to alternate.
ZAP: Setting this bit high forces the ZEN out­
put low. This bit is low to allow normal opera­
tion of the ZEN output.
B1S2, B1S1, B1S0: B1 Trigger SOURCE
select bits. Bit encoding is the same as the
encoding for the A Trigger SOURCE select
bits.
REV OCT 1991
Theory of Operation—2246 1Y and 2246 Mod A Service
SOURCE
CH 1
CH 2
CH 1 + CH 2
CH 3
CH 4
Line
—
VERT MODE
for display; it
B2S2, B2S1, B2S0: B2 Trigger SOURCE
select bits. Encoded the same as A Trigger
SOURCE select bits, except that code 111
does not select VERT Mode trigger. Selection
between B1 SOURCE and B2 SOURCE is nor­
mally made with the DS (delay select) output
signal. DS = 1 selects B1, and DS = 0 selects
B2. If the B1 select bits are 111 and the B1
SOURCE is selected (not fo rce d ), then the
data on output pins BTS2, BTS1, and BTSO
will track with the selected vertical channel
(similar to the A Trigger SOURCE select out­
puts) .
B1 SLOPE, B2 SLOPE: B Trigger SLOPE bits.
One of these two bits is presented on the B
SLOPE output pin (if B SLOPE isn't being
fo rce d ), in the same way that the B1 and B2
sources are selected. When B1 SOURCE is
selected, then B1 SLOPE is also selected,
and B2 SLOPE gets selected when B2
SOURCE is selected.
VM1, VMO: Vertical MODE control bits. See
Table 3-12 for encoding.
Table 3-12

Vertical MODE Select

VM1 VMO
0 0 Not used
0 1
Chop Mode
1 0
Alt Mode (with no measurement)
1 1
Alt Mode (with measurement)
HM1, HMO: Horizontal MODE control bits.
See Table 3-13 for encoding.
Table 3-13

Horizontal MODE Select

HM1
HMO
0
0
0
1
1
0
1
1
MODE
MODE
A only
ALT
B only
X-Y
3-21