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SECTION III
PROGRAMMING
3.1 GENERAL
This section contains information about the terminal for use in designing a service routine
to
perform special functions required
by
specific applications
of
the terminal. The information
is
directed
to
personnel who are actively involved in programming the Model
990
Computer.
Therefore,
the
section's presentation assumes
that
the reader
is
familiar with the programming
information contained in
the
Model 990 Computer Assembly Language Programmer's Guide
concerning
both
the
computer
and the terminal.
3.2 TERMINAL
CONTROLLER INTERFACE
The interface between the
computer
and a VDT controller consists
of
32
addressable
input
bits
and
32
addressable
output
bits. Each controller contains logic for one
or
two
video display units.
Input
and/or
output
bits are addressed
by
software
as
follows:
• Software sets the CRU base address for the desired keyboard/display unit.
• Software writes a 1
or
0
to
CRU bit F 16 to select
the
desired
16
bits
onto
the
CRU
interface.
• Software initiates a read
or
write
to
or
from the desired CRU bit address.
Corresponding bits for
the
keyboard/display units have identical meanings. Software
is
responsi-
ble for
proper
selection.
3.2.1 INPUT INTERFACE. The addressable input data
to
the
computer
includes
the
display
memory read character, a character intensity bit, keyboard character data, cursor address, and
status and error signals. The input interface signals are illustrated in figures
3-1
and 3-2 and
defined in table 3-1.
3.2.2
OUTPUT INTERFACE. The addressable
output
data from the
computer
includes display
memory write data, test control bits, character intensity bit, write data strobe, cursor controls,
interrupt enables, a word select bit and a cursor address. Figures 3-4 and 3-5 illustrate and
table 3-3 defines the
output
interface.
3.3
SCREEN INITIALIZATION
Following a
computer
power-up sequence
or
execution
of
a reset instruction, the screen
is
blanked, and the cursor
is
homed. The following conditions exist:
•
Monitor screen blank
•
Cursor at row 0, column 0
•
Keyboard interrupts inhibited
•
Interrupts reset
•
Test mode reset
•
Cursor blanked and
not
blinking
•
Dual intensity feature disabled.
3-1
Digital Systems Division
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