RG82845M Intel, RG82845M Datasheet - Page 106

• Manufacturer Part Number: RG82845M
• Description: Chipset Memory Controller Hub Mobile
• Manufacturer: Intel

Intel
4.1.1.
106
Figure 6. Detailed DOS Compatible Area Address Map
®
82845MP/82845MZ Chipset-Mobile (MCH-M)
Note: The VGA_EN bit may be set in the BCTRL registers. Software must not set more than one of the
VGA and MDA Memory Space
Video cards use the VGAA, MDA, and VGAB legacy address ranges defined above to map a frame
buffer or a character-based video buffer. By default, accesses to these ranges are forwarded to hub
interface. However, if the VGAEN bit is set in the BCTRL1 configuration register, then transactions
within these VGA and MDA memory spaces are sent to AGP instead of the hub interface.
VGA_EN bits.
If the configuration bit MCH-MCFG.MDAP is set, then accesses that fall within the MDA range
(0B0000h – 0B7FFFh) will be sent to hub interface without regard for the state of the VGAEN bit (but
accesses to the VGAA and VGAB ranges will still be sent to AGP). Legacy support requires the ability
to have a second graphics controller (monochrome) in the system. In an Intel 845MP/845MZ Chipset
system, accesses in the standard VGA range are forwarded to AGP when VGAEN is set. Since the
monochrome adapter may be on the hub interface bus (or other expansion bus), the MCH-M must be able
to decode cycles in the MDA range and forward them to the hub interface. This capability is controlled
by the MDAP configuration bit. In addition to the memory range B0000h to B7FFFh, the MCH-M can
decode I/O cycles at 3B4h, 3B5h, 3B8h, 3B9h, 3BAh, and 3BFh and forwards them to hub interface.
Standard PCI/ISA
Key
(SMM Memory)
Video Memory
VGAA
VGAB
MDA
= Optionally AGP
= Optionally DRAM
= DRAM
0A0000h
0C0000h
0B8000h
0B0000h
From
Datasheet
Expansion Card BIOS
Monchrome Display
and Buffer Area
Adapter Space
Upper, Lower,
0_000A_0000
0_000B_0000
0_000B_8000
1MB
768 KB
736 KB
704 KB
640 KB
To
0_000A_FFFF
0_000B_7FFF
0_000B_FFFF
C o n t r o l l e d b y
PAM[6:0].
C o n t r o l l e d b y
VGA Enable and
MDA enable.
250687-002
R