Tandy 1000 Technical Reference Manual

Tandy 1000
Technical Reference Manual
Mode Register (308)
This mode register controls the basic operating characteristics of the video.
It consists of a 6-bit write-only register, and each bit controls one aspect of
the operation of the video subsystem.
Bit Description
o High Resolution Dot Clock. This bit controls the operating speed of the
video system. A
"0" selects the lower speed for 40 character text or
low resolution graphics modes. A "1" selects high speed for 80 character
text or high resolution graphics modes.
Graphics
Select. This bit selects alpha or graphics modes. A "0" selects
the alpha mode. A
"1" selects the graphics mode.
2 Black and White Select.
This bit selects black and white or color mode
for
TV or composite monitors. A "1" will disable the color signal and
give a black and white image.
In RGB monitors, a different color palette
is selected by this bit in 320 x 200 4 color graphics mode. This bit will
have no other effect on RGB operation.
3 Video Enable.
This bit enables or disables the video display. A "1"
enables the video display.
4 640 Dot Graphics.
This bit is used to select either of the two 640 x 200
graphics modes. A
"1" selects 640 x 200.
5 Blink Enable. This control bit is used in the alpha mode only. A "1" selects
blinking
if the attribute bit is set (bit 7). A "0" selects 16 background
colors.
(With blinking selected only 8 background colors are available.)
Color Select Register (309)
This register is used to control several color features in the alpha modes and
the 320 x 200 4 color mode.
Bit Description
0-3 Alpha Border. In either alpha mode, these bits are used to select the
screen color.
In the 320 x 200 4 color mode, these bits determine the
background color
if PAO and PA 1 are both O. In the 640 x 200 2 color
mode, they select the foreground color.
o Blue
Green
2
Red
3 Intensity
4 Alpha Background/320 Graphics Foreground Intensity.
When blink is
enabled in the alpha mode, this bit is used to select the intensity. In the
320 x 200 4 color mode, the bit selects the intensity of the foreground.
5 320 x 200 4 Color Blue Control.
This bit is used to control the blue out-
put
in 320 x 200 color graphics.
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Tandy 1000 Specifications

General

Processor	Intel 8088
Processor Speed	4.77 MHz
RAM	128 KB (expandable to 640 KB)
Operating System	MS-DOS 2.11
Manufacturer	Tandy Corporation
Release Year	1984
Storage	Single or double 5.25" floppy disk drive (360 KB), optional hard drive
Sound	Tandy 3-voice sound
Ports	Parallel, Serial
Graphics	CGA (Color Graphics Adapter)
Graphics Modes	320x200, 640x200