Texas Instruments 990 Installation And Operation Manual page 43

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945423-9701
Bit Number
Table 3-3. Model 911 YDT Controller Addressable Output Bits (Continued)
Description
Cursor Address - provides the cursor address for the display memory. Bit 0 or 10 is
the least significant bit position while Bit AI6 or lAI6 is the most significant bit
position. Bits BI6 and 1 BI6 are reserved for address expansion. When the cursor ad-
dress is altered, data in the new address is read by the controller into the read data
register. Cursor address changes are detected when CRU bit AI6 (or lA 16 ) is written.
Consequently, this bit must be output regardless of the number of address bits trans-
ferred. Note that the most significant cursor bit is bit 9 for 960-character displays.
Bit A 16 , always zero, must still be output.
Only cursor addresses between 0 and 3BF 16 are displayed on the 960-character
screen. Cursor addresses between 0 and 77F 16 are displayed on the 1920-character
screen. The nondisplayed locations may be used by the programmer or in the program.
If the cursor address points to a nondisplayed location, the cursor will disappear from
the screen.
Not used.
Display Cursor - controls the indication of a cursor on the screen. Turning the cursor
off permits it to be moved on the screen without causing annoying flashes from
momentary cursor positions. A logic 1 enables a cursor indication, while a logic 0
blanks the cursor. An I/O reset instruction or a power-up reset sets display cursor
to logic O.
Keyboard Acknowledge - resets the keyboard data ready flag, keyboard interrupt (if
enabled), and the keyboard parity error flag. This output causes a strobe when ad-
dressed and is independent of the data value output. Data may be logic 0 or 1. An
I/O reset instruction on power-up reset condition effectively forces a keyboard ac-
knowledge strobe.
Beep Enable Strobe - causes an audible "beep" at the VDT. Addressing this bit with
a logic 0 or 1 data bit results in the generation of a O.3-second tone at 2000 Hertz.
Select Word - The functIon of any CRU interface bit is determined by the type of
operation (input or output) and the select word state (logic 0 or 1). Figures 3-1 and
3-2 and 34 and 3-5 show the two functions assigned to each input and output bit.
The 32 input and 32 output bits on the CRU interface associated with each video
display terminal are grouped into 16-bit words. The first set of inputs or outputs is
selected by setting select word = O. The second set of inputs or outputs is selected
by setting select word = 1.
3-11
Digital Systems Division