Tandy 1000 Technical Reference Manual

Tandy 1000
Technical Reference Manual
Video Memory Map and Registers
Video Memory Map
Address Description
300 Not used
301 Not used
302 Not used
303 Not used
304 6845 Address Register
305 6845 Data Register
306 Not used
307 Not used
308 Mode Select Register
309 Color Select Register
30A Video Array Address & Status
30B Clear Light Pen Latch
30C Set Light Pen Latch
300 Not used
30E Gate Array Data
30F CRT Processor Page Register
Operation
of the video subsystem and mode selection is controlled by the
registers listed
in the above table. The video array registers at 30A were ex-
plained earlier. The remaining control registers operate as follows:
6845 Address Register (304)
This 5-bit write-only register addresses 1 of the 18 internal data registers of
the 6845 CRT controller. The selected register is then read or written through
the 6845 data register.
6845 Data Register (305)
This port is used to access the internal data register previously selected through
the 6845 address register.
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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