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Section 2. System Board
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
Microprocessor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
Cache Memory Operation .................... 2-2
Cacheable Address Space .................... 2-3
Bus Adapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3
Keyboard/Mouse Connector . . . . . . . . . . . . . . . . . . . . . 2-4
Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
Scan Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5
Keyboard ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6
Displayable Characters and Symbols .............. 2-7
Hard Disk Drive Connector ..................... 2-8
External Bus Connector ....................... 2-9
UltraBay II Connector ....................... 2-12
Diskette Drive and Controller ................... 2-15
Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-16
ROM Subsystem . . . . . . . . . . . . . . . . . . . . . . . . 2-16
RAM Subsystem . . . . . . . . . . . . . . . . . . . . . . . . . 2-16
System Memory Map ...................... 2-17
System Board Memory for the DIMM Connectors ..... 2-18
RT/CMOS RAM . . . . . . . . . . . . . . . . . . . . . . . . . 2-19
RT/CMOS Address and NMI Mask Register (Hex 0070) 2-20
RT/CMOS Data Register (Hex 0071) ........... 2-20
RT/CMOS RAM I/O Operations .............. 2-21
CMOS RAM Configuration ................. 2-25
Miscellaneous System Functions and Ports .......... 2-29
Nonmaskable Interrupt (NMI) ................. 2-29
System Control Port A (Hex 0092) .............. 2-30
System Control Port B (Hex 0061) .............. 2-31
Power-On Password . . . . . . . . . . . . . . . . . . . . . . 2-32
Other Passwords . . . . . . . . . . . . . . . . . . . . . . . . 2-32
Selectable Drive-Startup Sequence .............. 2-33
Hardware Compatibility . . . . . . . . . . . . . . . . . . . . . . 2-34
Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-35
Copyright IBM Corp. 1997 2-1