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VCOUNT_BY2
ADDR_CNT_BY2
WRAP_A15TOA0
BYTE_MODE
CRTC_SYNC_EN
CRT Mode Register
Field Name
LINE_CMP
Line Compare Register
Field Name
GRPH_DEC_RD1
Graphics Controller Index Decode Register
Field Name
GRPH_DEC_RD0
Graphics Controller Index Decode Register
Field Name
GRPH_LATCH_DATA
RAM Data Latch Readback Register
© 2007 Advanced Micro Devices, Inc.
Proprietary
2
0x0
Vertical_by_2
NOTE: When bit 2 is logical one, other vertical register values should
be adjusted as well (CRT06, CRT10, CRT12, CRT15, and CRT18).
3
0x0
Count_by_2: ENGINEERING NOTE: Bit can be written and read, but
has no effect.
5
0x0
Address Wrap: ENGINEERING NOTE: Bit can be written and read,
but has no effect.
6
0x0
Byte/Word Mode:
0=WordMode
1=ByteMode
7
0x0
H/V Retrace Enable:
0=Disable HVSync
1=EnaHVSync
CRT18 - RW - 8 bits - VGACRTIND:0x18
Bits
Default
7:0
0x0
- These bits are the eight low-order of the 10-bit line compare regis-
ter. Bit 8 is CRT07[4], bit 9 is CRT09[6]. The value of this register is
used to disable scrolling on a portion of the display screen, as when
split screen is active. When the vertical counter reaches this value,
the memory address and row scan counters are cleared.- The screen
area above the line specified by the register is commonly called
screen A. The screen below is screen B. Screen B cannot be
scrolled, but it can panned only together with screen A, controlled by
the PEL panning compatibility bit ATTR10[5]. (For a description of
this control bit see ATTR10[5].)
CRT1E - R - 8 bits - VGACRTIND:0x1E
Bits
Default
1
0x0
This register is used to read back the graphics controller index
decode.
CRT1F - R - 8 bits - VGACRTIND:0x1F
Bits
Default
7:0
0x0
This register is used to read back the graphics controller index
decode.
CRT22 - R - 8 bits - VGACRTIND:0x22
Bits
Default
7:0
0x0
This register is used to read the data in the Graphics Controller CPU
data latches. The Graphics Controller Read Map Select register bits
0 and 1 determines which byte is read back.
VGA Registers
Description
Description
Description
Description
M56 Register Reference Manual
2-177
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