Radio Shack TRS-80 Model II Reference Manual page 203

Technical Information
VDREAD Video Read
(fnntion code 11)
This routine reads characters from the Video Display into a specified buffer.
It is a Graphics Mode routine; when it reads past the last column, it wraps
back to column 1 on the next row. When it reads past column 79 on row 23, it
wraps back to row 0, column O.
Reverse (black on white) mode characters are read in as
ASCII
codes just like
their Normal counterparts; Reverse mode is indicated when the,most
significant bit (bit 7) is set.
This routine can also be used just to locate the cursor (see below).
Entry Conditions
B
=
Row on screen where read starts, B < 24
If B > 23, then B mod 24 is used as row position.
C =
Column on screen where read starts
In 80 character/line mode, C < 80
For C >79, C mod 80 is used as column position.
In 40 character/line mode, C < 40
For C > 39, C mod 40 is used as column position.
D = Length of buffer, in range [0,255]. If D = 0, then Band Care
ignored. Current cursor position will be returned as row, column in
BC register pair.
(HL) =
Beginning of text buffer
A = 11
Exit Conditions
BC
=
NZ=
A=
Current cursor position, B = row, C = column.
CURSOR
position at
exit is the same as at entry -
VDREAD
does not change it.
Error
Error Code
239