Radio Shack TRS-80 Model II Reference Manual page 206

Model II
TRSDOS
VIDRAM
Transfer Video Display to
RAM
or Vice-Versa
(function code 94)
This command allows a screenful of graphics and/or text to be copied from a
RAM
buffer to the video display, or vice-versa. The programmer must be aware of the
current display mode-80 characters/line or 40 characters/line.
Every possible data byte is treated as a displayable character. There are no cursor
position or other control codes. The following table summarizes the character/code
relationships for this routine:
Hex Code
OO-IF
20-7F
80-9F
AO-FF
Display Character
Normal Graphics
Normal
ASCII
Text
Reversed Graphics
Reversed
ASCII
Text
Entry Conditions
A =94
B
=
Function Code
If B
=
0, copy from
RAM
to video
IfB
*'
0, copy from video to
RAM
(HL)
=
RAM
Buffer. Start of buffer must be above
X'2800';
end of buffer must be
below
X'FOOO'.
If video is in 80 cpl mode, buffer must be 80
*
24
=
1920 bytes long.
If video is in 40 cpl mode, buffer must be 40
*
24
=
960 bytes long.
Exit Conditions
The cursor position is unchanged by this
svc.
242