|
The CMOS RAM data area consists of two banks of 128 bytes.
The first 64 bytes in both bank are the same and contain clock and calendar
information. The second 64 bytes in bank 1 control security and system
start-up features.
Note: Access to the two banks in
CMOS RAM is controlled by the bank-control bit in Status Register A - see
Status Register A (Hex 00A).
RAM Address Map
ADDRESS DESCRIPTION
000-00D Real-Time Clock bytes
00E Diagnostic Status byte
00F Shutdown Status byte
010 Diskette Drive Type byte
011 First Fixed Disk Drive Type byte
012,013 Reserved
014 Equipment byte
015,016 Low and high Base Memory bytes
017,018 Low and high Expansion Memory bytes
019-031 Reserved
034 Reserved
035,036 Low and high usable memory above 1MB
037 Date Century byte
038-07F Reserved
Warning! The operation that follows a
write operation to address hex 0070 must read from address hex 0071; otherwise
intermittent malfunctions and unreliable operation of the RT/CMOS RAM can occur.
CMOS RAM Bank 0
000-00D Real-Time Clock Bytes
00A Status Register A Timer Related
00B Status Register B Date and Alarm Related
00C Status Register C Interrupt Related
00D Status Register D CMOS Valid Byte
CMOS RAM Configuration
00E Diagnostic Status Byte Configuration Related
00F Shutdown Status Byte Set by power-on diagnostics
010 FD Type Byte Type of Floppy installed
011 1st Fixed Disk Drive Type Byte Type HD installed
011 2nd Fixed Disk Drive Type Byte Type HD installed
012,013 Reserved Bytes
014 Equipment Byte #FDs, Display, Co-pro, A: present
015,016 Low and High Base Memory Bytes Memory <640KB
017,018 Low and High Expansion Memory Bytes Memory >1MB
019-031 Reserved Bytes
032,033 Configuration CRC Bytes CRC data for RTC CMOS
034 Reserved Byte
035,036 Low and High Usable Memory Bytes Memory 1-16MB
037 Date-Century Byte BCD Value for century
038-04F Reserved Bytes
CMOS RAM Bank 1
40-47F System Number System Identifier
48 Century Byte BCD Value for Century
49 Wake-up Alarm Date Date set for Power-On
4A Extended Control Register A Security and power-on
4B Extended Control Register B Security and power-on
4C-7F Reserved
|