Tandy 1000 Technical Reference Manual

Tandy 1000
MC6845
OPERATION OF THE CRTC
Technical Reference Manual
Timing Chart of the CRT Interface Signals - Timing
charts
of CRT interface signals are illustrated in this
section with
the aid of programmed example of the
CRTC. When values listed in Table 4 are programmed into
CRTC control registers,
the device provides the outputs as
shown
in the Timing Diagrams (Figures 13 through 15).
The screen
format of this example is shown in Figure 9.
Figure 16 is an illustration of the relation between
Refresh Memory Address (MAO-MA 13), Raster Address
(RAO·RA4)
and the position on the screen. In this
example,
the start address is assumed to be "0".
TABLE 4 - Values Programmed Into CATe Registers
Reg. #
Programmed
Register Name Value
Value
AO H. Total
Nht+
l
Nht
Al
H. Displayed
Nhd
Nhd
A2 H. Sync Position
Nhsp
Nhsp
A3
H. Sync Width
Nhsw
Nhsw
A4 V. Total
N
vt
+1
N
vt
AS V. Scan Line Adjust
Nadj
Nadj
A6
V. Displayed
NVd
NVd
A7 V. Sync Posit ion N
vSp
N
vsp
AS
Interlace Mode
A9
Max. SCan Line Address
Nsl
Nsl
A10
Cursor Start
All Cursor End
A12 Start Address (H)
AI3 Start Address (L)
A14
Cursor (H)
AIS
Cursor (L)
A16
Light Pen (H)
Al7
Light Pen fL)
® MOTOROLA SelTliconductor Products Inc.

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