Tandy 2000 Service Manual page 288

Tandy@
Model
2000
Service
Manual
Below is a chart for the bits contained in the plane select
register.
BIT
0
I
2
3
4
5
6and7
FUNCTION
Select plane
0
Se1ect plane I
Select plane
2
No
connection
Graph
ics
on/ of
f
Graphic
s/
atpha
swi
tch
No connection
To
select
a
particular
plane, d 1
must be
in
the
corresponding
bit
while the
remaining two prane serects
are
a
0. If
plane
I is to
be
selected,
then
D0
and
D2 would
contain
a
0,
while DI
would
contain a
1.
The
graphics on/off bit,
D4, contains a 1 to turn
on
(display) the graphics data in the installed
planes.
A
0
forces the palette to ignore the
memory
plane data
and
display the color
contained
at palette
address
08H
(Processor I/0
address
0190H).
The
graphics,/alpha bit ,
D5, determines which
data is
used
as
palette addresses. If this bit is a I, the
Hi-Res
memory
planes are used. If this bit is a 0, the
9007
video data is
used
(this displays text
on
the
Cl*{-l
color monitor).
9.
3.5 Displaying
Alpha-Numeric Text
The Hi-Res board contains circuitry to switch
between the
internal
memory
planes or external data for
use as
palette
addresses. In the
l,todel 2000,
the external data is
hard-wired on the
bus
as the
9007
video
and
the
video
attribute bit
rNTENsrrY. rf the external
mode
is
selected
(referred to as the
ALPHA
I{ODE),
the video data is palette
address
bit
A0 and
the attribute bit for intensity is
palette
address
bit A1. palette
address
bits
A2 and A3 are
tied high (a 1). This allows -color text to
be displayed
on
the C!I-I color
monitor.
For this to
work
properly, the
9007
must be
in
640
X
400
display
mode,
NOT
in
800
X
400
mode. Text
from
the
9007
and
graphics data from the
Hi-Res board
CANNOT
be displayed at
the
same
time
on
the
CM-1
monitor.
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