Acrosser AR-B1551 - Manual (Page 11)

AR-B1551 User’s Guide
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2.4.2 Real-Time Clock and Non-Volatile RAM
The AR-B1551 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 periods of time using an internal Lithium battery. The contents of each byte in
the CMOS RAM are listed as follows:
Real-Time Clock & Non-Volatile RAM
2.4.3 Timer
The AR-B1551 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.
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