Sony 486DX User Manual
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:
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.
Application programs can load different counts into this timer to generate various sound frequencies.