RT/CMOS RAM
The RT/CMOS RAM (real-time clock/complementary metal-oxide
semiconductor RAM) module contains the real-time clock and 128
bytes of CMOS RAM. The clock circuitry uses 14 bytes of this
memory; the remainder is allocated to configuration and
system-status information. A battery is built into the module to keep
the RT/CMOS RAM active when the power supply is not turned on.
In addition to the 128 bytes of CMOS/RAM, a CMOS/RAM extension
of 4 KB is provided for configuration and other system information.
Figure 2-13 lists the RT/CMOS RAM bytes and their addresses.
Figure 2-13. RT/CMOS RAM Address Map
Address (Hex) RT/CMOS RAM Bytes
000–00D Real-time clock
00E Diagnostic status
00F Shutdown status
010 Diskette drive type
011 Hard disk 2 and 3 drive type
012 Hard disk 0 and 1 drive type
013 Reserved
014 Equipment
015, 016 Low and high base memory
017, 018 Low and high expansion memory
019 Hard disk 0 extended byte
01A Hard disk 1 extended byte
01B Hard disk 2 extended byte
01C Hard disk 3 extended byte
01D–02D Reserved
02E, 02F Checksum
030, 031 Low and high usable memory above 1 MB
032 Date-century
033–07F Reserved
2-18 System Board
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