IBM 6268 Personal Computer User Manual


 
Appendix B. System address maps
Appendix B. System address maps
System memory map
The first 640 KB of system board RAM is mapped starting at address hex 0000000. A 256 byte area and
a 1 KB area of this RAM are reserved for BIOS data areas. Memory can be mapped differently if POST
detects an error.
Input/output address map
The following figure lists resource assignments for the I/O address map. Any addresses that are not
shown are reserved.
Figure 33. System memory map
Address range (decimal) Address range (hex) Size Description
0 K – 512 K 00000–7FFFF 512 KB Conventional
512 K – 639 K 80000–9FBFF 127 KB Extended conventional
639 K – 640 K 9FC00–9FFFF 1 KB Extended BIOS data
640 K – 767 K A0000–BFFFF 128 KB Dynamic video memory
display cache
768 K – 800 K C0000 to C7FFF 32 KB Video ROM BIOS
(shadowed)
800 K – 896 K C8000–DFFFF 96 KB PCI space, available to
adapter ROMs
896 K – 1 MB E0000–FFFFF 128 KB System ROM BIOS (main
memory shadowed)
1 MB – 16 MB 100000–FFFFFF 15 MB PCI Space
16 MB – 4095.872 MB 1000000–FFF7FFFF 4079.5 MB MB PCI Space (positive decode)
FFF80000 –FFFFFFFF 512 KB System ROM BIOS
Figure 34 (Page 1 of 3). I/O address map
Address (Hex) Size Description
0000–000F 16 bytes DMA 1
0010–001F 16 bytes General I/O Locations — available to PCI bus
0020–0021 2 bytes Interrupt controller 1
0022–003F 30 bytes General I/0 locations — available to PCI bus
0022–002F 2 bytes SMC SIO index/data register
0040–0043 4 bytes Counter/timer 1
0044–00FF 28 bytes General I/0 locations — available to PCI bus
0060 1 byte Keyboard controller byte - reset IRQ
0061 1 byte PIIX4, System port B
0064 1 byte Keyboard controller, CMD/STAT byte
0070, bit 7 1 bit Enable NMI
0070, bits 6:0 1 bit Real time clock, address
0071 1 byte Real time clock, data
0072–007F 14 bytes General I/O locations — available to PCI bus
36 Copyright IBM Corp. September 1999