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AR-B1551 User’s Guide

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

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 ... 36 37

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Acrosser AR-B1551 Manuel d'utilisateur Page 12

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