Aaeon PCM-4330 Instructions Manual page 84

A MC146818A compatible, battery-buffered real-time clock (RTC) is included in
the DC37C92x-Ultra-I/O-controller. It provides data for time, alarm, control and
status information. The remaining RAM is used by the BIOS to store system configu-
ration data.
Table26 illustrates the internal
RTC port addresses
To the programmer the RTC
apears as a 128 byte RAM area
that can be addressed via two I/O
addresses. 192 bytes RAM are in
this address-area. Two RAM
pages are in area 40h to 3Fh which
may be paged in/out alternatively.
Writing into the RTC requires two steps:
[1] Address output (OUT) at port70h
[2] Data output (OUT) at port 71h
Note to programmers: Accessing port 70h, databit 7 determines the
i
status of the NMI controller:
Bit 7 = 1, NMI disabled
Bit 7 = 0, NMI enabled
The desired control status for the NMI must be set for every applica-
tion program accessing the RTC!
00h Second
01h Seconds-Alarm
02h Minutes
03h Minutes-Alarm
04h Hours
05h Hours-Alarm
06h Day of Week
07h Day of Month
08h Month
09h Year
0Ah Status Register A
0Bh Status Register B
0Ch Status Register C
0Dh Status Register D
0Eh-3Fh 50 bytes used by BIOS
40h-7Fh 2*64 bytes used by BIOS
0-59
0-59
0-59
0-59
1-12(24)
0-23
1-7
1-31
1-12
0-99