Texas Instruments 990 Installation And Operation Manual page 36

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945423-9701
Bit Number
7
16 ,
17
16
Table 3-1. Model 911 VDT Controller Addressable Input Bits
Description
NOTE
Select Word (bit F
16
or 1 F
16)
must be set to 0 for the following bit definitions.
Display Memory Read Data - VDT memory data read from memory address defined
by current cursor location. Following a power-up sequence, a write operation or cur-
sor address change must occur before the read data is ready for access.
Dual Intensity - selects the intensity level for the VDT display. Logic 0 selects the
high level of intensity; logic 1 selects the low intensity level when dual mode is an
active feature. On Japanese Model 911 's, all characters are displayed at high intensity;
bits 7
16
and 17
16
are used to select Katakana (logic 1) or alphanumeric (logic 0).
Keyboard Data - least significant seven bits of keyboard character received from the
VDT display unit keyboard. An 8-bit character is required to accommodate the full
ASCII character set (128 characters) and additional special function keys. The key-
board control bit is in word select 1, CRU bit B
16 .
Keyboard Data Ready - logic 1 indicates a character has been input at the display
keyboard and is available to be read by the CPU. This signal is reset to logic 0 by an
output of Keyboard Acknowledge. Keyboard Data Ready may be read independent
of the word-select control bit.
NOTE
The VDT controller may generate two CRU interrupts - one for each display.
An interrupt Signal occurs as a result of the keyboard ready signal if the key-
board interrupt and enable control associated with a display is set to logic 1.
NOTE
Select Word (Bit F
16
or 1F
16 )
must be set to 1 for the following bit defini-
tions.
Cursor Address - indicates the position of the cursor on the screen. The cursor in-
dicates the position of the-next character to be placed on the VDT screen. The number
of address bits used is determined by the total number of character positions on the
screen. Ten address bits are used with 960 character displays; 11 address bits are used
with 1920 character displays. An unused address bit is always read as zero. The range
of addresses for the 960 and 1920 character displays is shown in figure 3-3. Note that
the display memory address range exceeds the range of the screen display. Memory
beyond the screen display address range is program-accessible, but is not displayed.
Keyboard Data Control Bit - MSB of keyboard character.
3-4
Digital Systems Division