Section Iii. Programming; General; Terminal Controller Interface; Screen Initialization - Texas Instruments 990 Installation And Operation Manual

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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