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AR-B1474 User¡¦s Guide
2-4
2.3.2 Real-Time Clock and Non-Volatile RAM
The AR-B1474 contains a real-time clock compartment that maintains the date and time in addition to storing
configuration information about the computer system. It contains 14 bytes of clock and control registers and 114
bytes of general purpose RAM. Because of the use of CMOS technology, it consumes very little power and can be
maintained for long period of time using an internal Lithium battery. The contents of each byte in the CMOS RAM
are listed as follows:
Address Description
00 Seconds
01 Second alarm
02 Minutes
03 Minute alarm
04 Hours
05 Hour alarm
06 Day of week
07 Date of month
08 Month
09 Year
0A Status register A
0B Status register B
0C Status register C
0D Status register D
0E Diagnostic status byte
0F Shutdown status byte
10 Diskette drive type byte, drive A and B
11 Fixed disk type byte, drive C
12 Fixed disk type byte, drive D
13 Reserved
14 Equipment byte
15 Low base memory byte
16 High base memory byte
17 Low expansion memory byte
18 High expansion memory byte
19-2D Reserved
2E-2F 2-byte CMOS checksum
30 Low actual expansion memory byte
31 High actual expansion memory byte
32 Date century byte
33 Information flags (set during power on)
34-7F Reserved for system BIOS
Table 2-3 Real-Time Clock & Non-Volatile RAM
2.3.3 Timer
The AR-B1474 provides three programmable timers, each with a timing frequency of 1.19 MHz.
Timer 0 The output of this timer is tied to interrupt request 0. (IRQ 0)
Timer 1 This timer is used to trigger memory refresh cycles.
Timer 2 This timer provides the speaker tone.
Application programs can load different counts into this timer to generate various sound frequencies.