Integrated Functions (Continued)
4.5.12 Cursor Position Registers
•
Display Controller Vertical Line Count
(DC_V_LINE_CNT)
The Cursor Position Registers contain pixel coordinate
information for the cursor. These values are not latched by
the timing generator until the start of the frame to avoid
tearing artifacts when moving the cursor.
-
This register is read only. It provides the current
scanline for the display. It is used by software to time
update of the frame buffer to avoid tearing artifacts.
•
•
Display Controller Cursor Y Position (DC_CURSOR_Y)
The Cursor Position group consists of four 32-bit registers
located at GX_BASE+8350h-835Ch. These registers are
described below and Table 4-33 gives their bit formats.
-
Contains the Y position information of the hardware
cursor.
Display Controller Split-Screen Line Compare
(DC_SS_LINE_CMP)
•
Display Controller Cursor X Position (DC_CURSOR_X)
-
Contains the X position information of the hardware
cursor.
-
Contains the line count at which the lower screen
begins in a VGA split-screen mode.
Table 4-33. Display Controller Cursor Position Registers
Bit
Name
Description
GX_BASE+8350h-8353h
DC_CURSOR_X Register (R/W)
Default Value = xxxxxxxxh
31:16
15:11
RSVD
Reserved: Set to 0.
X_OFFSET
X Offset: This field represents the X pixel offset within the 32x32 cursor pattern at which the displayed
portion of the cursor is to begin. Normally, this value is set to zero to display the entire cursor pattern, but
for cursors for which the "hot spot" is not at the left edge of the pattern, it may be necessary to display
the rightmost pixels of the cursor only as the cursor moves close to the left edge of the display.
10:0
CURSOR_X Cursor X: This field represents the X coordinate of the pixel at which the upper left corner of the cursor
is to be displayed. This value is referenced to the screen origin (0,0) which is the pixel in the upper left
corner of the screen.
GX_BASE+8354h-8357h
DC_V_LINE_CNT Register (RO)
Reserved (Read Only)
Default Value = xxxxxxxxh
31:11
10:0
RSVD
V_LINE_CNT Vertical Line Count (Read Only): This value is the current scanline of the display.
(RO)
Note: The value in this register is driven directly off of the DOTCLK, and consequently it is not synchronized with the CPU clock. Soft-
ware should read this register twice and compare the result to ensure that the value is not transitioning.
GX_BASE+8358h-835Bh
DC_CURSOR_Y Register (R/W)
Default Value = xxxxxxxxh
31:16
15:11
RSVD
Reserved: Set to 0.
Y_OFFSET
Y Offset: This field represents the Y line offset within the 32x32 cursor pattern at which the displayed
portion of the cursor is to begin. Normally, this value is set to zero to display the entire cursor pattern, but
for cursors for which the "hot spot" is not at the top edge of the pattern, it may be necessary to display
the bottommost lines of the cursor only as the cursor moves close to the top edge of the display. Note
that if this value is nonzero, the CUR_START_OFFSET must be set to point to the first cursor line to be
displayed.
10
RSVD
Reserved: Set to 0.
9:0
CURSOR_Y Cursor Y: This field represents the Y coordinate of the line at which the upper left corner of the cursor is
to be displayed. This value is referenced to the screen origin (0,0) which is the pixel in the upper left cor-
ner of the screen.
This field is alternately used as the line-compare value for a newly-programmed frame buffer start offset.
This is necessary for VGA programs that change the start offset in the middle of a frame. In order to use
this function, the hardware cursor function should be disabled.
GX_BASE+835Ch-835Fh
DC_SS_LINE_CMP Register (R/W)
Reserved: Set to 0.
SS_LINE_CM Split-Screen Line Compare: This is the line count at which the lower screen begins in a VGA split-
screen mode.
Default Value = xxxxxxxxh
31:11
10:0
RSVD
P
Note: When the internal line counter hits this value, the frame buffer address is reset to 0. This function is enabled with the SSLC bit
in the DC_GENERAL_CFG register.
Revision 3.1
149
www.national.com
NSC [ National Semiconductor ]
