Tandy 1000 HX Technical Reference Manual page 419

ROM BIOS Data Area
The structure and usage of the Video driver RAM data area is
as follows:
29
The following table gives the starting offset, and length of each
BIOS device driver. This area is located at segment 40:00.
Comm card addresses
Printer addresses
Devices installed
Not used
Memory size
I/O channel RAM size
KBD data area
Disk data area
Video data area
Not used
Clock data area
0000
0008
0010
0012
0013
0015
0017
003E
0049
0067
006C
KBD Break & Reset flags0071
Not used
Printer Timeout counter
Comm Timeout counter
KBD extra data area
0074
0078
007C
0080
8 (1 word per card)
8 (1 word per printer)
2 (16 bits)
1
2 (1 word)
2 (1 word)
39
11
30
5
5
3
4
4 (1 byte per printer)
4 (1 byte per card)
4 (2 words)
HEX Offset From
Segment 0040:000
49H
4AH
4CH
4EH
50H
60H
62H
63H
65H
66H
Length and
Intended Use
1 byte - current CRT mode (0-7)
1 word - screen column width
1 word - byte length of screen
1 word - address/offset of beginning
of current display page
8 words - row/col coordinates of the
cursor for each of up to 8
display pages
1 word - current cursor type (See "set
cursor type" for correct
encoding)
1 byte - current display page
1 word - base address + 4 of the
CRT controller card
1 byte - copy of value written to the
Mode Select Register
1 byte - current color palette setting