Character Pixel Arrangement; Field And Mixer Attribute Bit Assignment - Tektronix 2246 1Y Service Manual

Theory of Operation—2246 1Y and 2246 Mod A Service
MIX3 MIX2 MIX1 MIXO
X X X
0
X X
0
X X
1
X X
1
X X
0 0
X
0 1
X
1 0
X
1
0
X
HORIZONTAL CURSOR MODE. The vertical output
displays vertical text information, whose position is
controlled by an analog cursor level control. The
horizontal output displays horizontal text information,
locked to crt horizontal screen position.
VERTICAL CURSOR MODE. The vertical output pro­
vides a ramp signal, locked to crt vertical screen
position. The horizontal output matches the voltage
of an analog cursor level control.
MIXER OPERATION. The readout system displays
text in a pixel-type representation. For example, an
underlined letter " A " may be represented as in
Figure 3-8. Blackened spaces in the illustration
denote a displayed pixel.
For each character, one pixel at a time is displayed
by driving the vertical and horizontal outputs to
values representing the vertical and horizontal
position of a pixel within the character and then
unblanking the Z-Axis.
Multiplexers U2414 and U2415 are ganged electronic
switches that mix current and voltage settings. Verti­
cal Readout DAC U2412 (vertical text generator)
provides an output current from
proportionate to the vertical position of the pixel
being displayed; the minimum output is 0 mA.
Horizontal Readout DAC U2413 (horizontal text gen­
erator) provides an output current that is pro­
portionate to the horizontal position of the pixel
being displayed. Its minimum output is also 0 mA.
The REF CURSOR and DELTA CURSOR levels are
voltages that offset the text output for the type of
cursor being displayed (vertical TIME cursors or hori­
3-50
Table 3-28
Field and Mixer A ttribute Bit Assignm ent
NC FLD2 FLD1
b2 bl
X X
0
X X X
1
X X X
0
X X X
1
X X X
X X
X X
X X X X
X X X X
X X X X
pin 2 that is
FLDO
bO Field number (0,1, or 2)
Route Horiz DAC to Horiz Ampl
X
Route CursorO to Horiz Amplifier
X
Route Cursorl to Horiz Amplifier
X
Unassigned
X
Route Vert DAC to Vert Ampl
X
Route Vert DAC + CursorO to Vert Amplifier
X
Route Vert DAC + Cursorl to Vert Amplifier
X
Route Horiz DAC to Vert Ampl
X
zontal VOLTS cursors). When straight text is to be
displayed, dc levels for offsetting the vertical and
horizontal text display outputs are added. Horizontal
and vertical signals to be mixed for a particular
readout are selected by the MIXO-3 outputs of latch
U2411. The data is latched from the Readout
Processor bus when MIX STB clock is generated by
the Readout Processor.
Output Buffers
The Output Buffers (U2416A and U2416D—vertical,
and U2416B and U24160—horizontal) are voltage
follower circuits that mix the signals selected by the
Readout Position Multiplexers and buffer them for
application to the vertical delay line (RO VERT) and
the Horizontal Preamplifier (RO HORIZ).
Figure 3-8. Character pixel arrangement.
Value
6081-11