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Real Time Clock (rtc) Ram; Real Time Clock (rtc)ram; Contents Of Rtc Ram - Mitsubishi Electric LS Pro Hardware Technical Reference

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Real time clock (RTC) RAM

The real time clock and its associated battery backed RAM is an MC146818. The RTC
RAM is accessed via I/O ports 0070h and 0071h. The first fourteen bytes are used to
store real time clock information, the remainder are used for system configuration
data.
The RTC is normally powered from the system +5V supply. However when the
computer is not switched on power is supplied by a rechargeable battery on
the system board. This maintains the correct time and configuration information.
If the battery becomes discharged the time and date will need to be reset and
the system will need to be reconfigured using the SETUP utility.
Contents of
The contents of the RTC RAM are listed below.
RTC RAM
Address
Real time clock data
00h
01h
02h
03h
04h
05h
06h
07h
08h
09h
0Ah
0Bh
0Ch
0Dh
0E
0F
Configuration data
10
11
12
13
14
15
Function
seconds
alarm seconds
minutes
alarm minutes
hours
alarm hours
day of week
date
month
year
status register A
status register B
status register C
status register D
Diagnostic Status
Shutdown code
Diskette drive type
Reserved
Fixed disk drive type
Power on password
Equipment byte
Base memory (low byte)
LS PRO HARDWARE TECHNICAL REFERENCE 3/11
System Board
Address
Function
16
Base memory (high byte)
Expected expanded memory
17
(low byte)
Expected expanded memory
18
(high byte)
19
Drive type for hard drive 0
1A-1E
Reserved
1F
shadow BIOS
20-27
Reserved
28
Apricot sound volume
29
Apricot options
2A
Apricot boot type
Apricot cache disable
2B
(see also byte 34h)
2C-2D
Reserved
2E
High byte checksum for 10-2D
2F
Low byte checksum for 10-2D
Actual expanded memory
30
(low byte)
Actual expanded memory
31
(high byte)
32
Century in BCD
Memory exceeds 512K/387
33
presence
486SLC cache control
34
(see also Apricot byte 2Bh)
35
Apricot access rights
36
Floppy/Token-Ring autodetect
37
Hard disk autodetect
38-3E
Power on password
3F
Byte checksum of bytes 38-3E

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