IBM RT Series Hardware Reference Manual page 326

TNL SN20-9844 (March 1987) to 75X0235
Y Cursor Register
I/O DATA FIELD
Bits 00-05 RESERVED
Bits 06-15 CURSOR LINE (lowest line of cursor box)
Figure 7. Y Cursor Register (Address X'D9F802')
Note: This register is initialized to X'FFFF' with a POR or reset adapter command.
This register is loaded by the system to specify the bottom scan line for the hardware supported
cursor. When the Y cursor register equals 0, the bottom most scan line of the cursor is displayed
on the first scan line on the screen (scan line 0). When the Y cursor register equals
767
+
63
=
830, then the top most scan line of the cursor is displayed on the last displayable
scan line of the screen (scan line 767). All other values of the Y cursor register between the top
and bottom numbers, position the cursor in all the other Y bit positions on the screen. If the Y
cursor register is greater than 831
=
767
+
64, then the cursor is not displayed.
14 Extended Monochrome Graphics Adapter
(