Position Enable Bit Assignment - Tektronix 2246 1Y Service Manual

11). See Table 3-27.
refreshed, the outputs of U2403 are enabled by the
POS EN signal from the Dot Refresher,
pin 19.
Table 3-27

Position Enable Bit Assignment

b4 b2 bl bO
b3
0
X X X
X
1
X X X X
0
X X X X
i
X X X
X
0
X X X . X
1
X
X X X
0
X X X X
1
X X X X
0
X X X X
1
X X X X
Readout DACs
Vertical Character and Dot position data bytes are
converted to analog current for eventual application
to the Vertical Delay Line by Vertical Readout DAC
U2412. The vertical signal current is applied to both
signal mixer multiplexers (U2414 and U2415). When
fixed position text is displayed, the output mixer
selects a fixed position value to mix with the hori­
zontal output signal to define the readout position on
the display. When positionable text is displayed
(such as time cursors), the cursor position signal is
mixed with the horizontal
summed signal then defines (vertically) where a
character (dot) is displayed on the crt. Vertical
Readouts that follow the Channel Vertical POSITION
controls (tracking cursors and associated text) have
their position information summed with the Vertical
Position Switching circuitry (Diagram 2) just before
the Delay Line Driver.
Theory of Operation—2246 1Y and 2246 Mod A Service
When a field is being
U2410
Value
Disable CH 1 position
current
Enable CH 1 position
current
Disable CH 2 position
current
Enable CH 2 position
current
Disable CH 3 position
current
Enable CH 3 position
current
Disable CH 4 position
current
Enable CH 4 position
current
Disable Trace Sep
current
Enable Trace Sep
current
output signal. That
Horizontal Character and Dot position data bytes are
converted to analog current for application to the
Horizontal Preamplifier (U802, Diagram 6) by Hori­
zontal Readout DAC U2413. The horizontal signal
current is applied to both signal mixer multiplexers
(U2414 and U2415). When fixed position text is dis­
played, the output mixer selects a fixed position
value to mix with the horizontal output signal to
define the readout position on the display. When
positionable text is displayed (such as time cursors),
the cursor position signal is mixed with the horizontal
character position signal. That summed signal then
defines (horizontally) where a character dot is
displayed on the crt. None of the readout (text or
cursors) is positionable
POSITION control.
Field and Mixer Control Latch
Selection signals for switching the Readout Position
Mixer multiplexers (U2414 and U2415) are latched
into Field and Mixer Control Latch U2411 by the MIX
STB output from the Readout Processor (U2400 pin
25). Three field selection bits used in addressing the
Character Code RAM are also loaded from the data
byte output from U2400 on the R0-R7 data bus. The
MIX3-MIX0 bits select the combination of fixed,
positionable, and character (dots) signals that are
mixed to produce the required readout positions on
the crt.
The Field signals (FLDO, FLD1, and FLD2) access
the type of characters that are displayed (menus
and readout labels, vertical cursors, or horizontal
cursors). Each of the three fields contains space for
255 characters. Characters from each field are
superimposable over the other field' s characters in
the display. The attributes implicitly affect the field
specified by bO, b l , and b2 (b2 is always handled as
if zero, even if not communicated as zero).
Readout Position Mixers
The Readout Position Mixer (U2414, U2415) selects
either fixed or cursor-position voltages to mix with
the character signals to position them in the display.
Selection is done with the MIX0-MIX3 signal levels
set by the Measurement Processor for the particular
field of characters
Table 3-28).
The 2246 1Y and 2246 Mod A Readout Output Mixer
allows three modes of display to present the text and
vertical or horizontal cursors.
TEXT OUTPUT MODE. The vertical output displays
vertical text information, locked to crt vertical screen
position. The horizontal output displays horizontal
text information, locked to crt horizontal screen
position.
using the Horizontal
being displayed (see
3-49