Radio Shack TRS-80 Model II Reference Manual page 205

Technical Information
If Z is not set (error), the registers Band C contain:
B
=
Number of characters not displayed, including the one causing the
error
C
=
Character causing the error
CURSOR
(function code 26)
This routine turns the blinking cursor on or off. The System still keeps track of
the current cursor position, whether it is on or off.
Entry Conditions
B
=
Function Switch. If B
=
0 then cursor will be turned off. If B < >0
then cursor will be turned on.
A= 26
SCROLL
~
(function code 27)
This routine lets you protect a portion of the Display from scrolling. From 0 to
22 lines at the top of the Display can be protected; when scrolling occurs, only
lines below the protected area will be changed.
Entry Conditions
B
=
Number of lines to be protected, in range [0,22].
A= 27
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