DIGITAL-LOGIC MICROSPACE MSM286 Series Technical User's Manual page 23

DIGITAL-LOGIC AG
4.16 Programmable timers
An 8253 compatible timer/counter device is also included in the board's ASIC device. This device is
utilized in precisely the same manner as in a standard AT implementation. Each channel of the 8253
is driven by a 1.190 MHz clock, derived from a 14.318 MHz oscillator, which can be internally divided
down to provide a variety of frequencies.
Timer 2 can also be used as a general purpose timer if the speaker function is not required.
Timer Assignment
Timer Function
0 ROM-BIOS clock tick (18.2 Hz)
1 DRAM refresh request timing (15 µS)
2 Speaker tone generation time base
4.17 Speaker interface
One of the board's CPU device provides the logic for a PC compatible speaker port. The speaker
logic signal is buffered by a transistor amplifier, and provides approximately 0.1 watt of audio power
to an external 8 ohm speaker.
4.18 Battery backed clock
An AT compatible date/time clock is located within the device BQ3285. The device also contains a
CMOS static RAM, compatible with that in standard ATs. System configuration data is normally
stored in the clock chip's CMOS RAM in a manner consistent with the convention used in other AT
compatible computers.
One unique feature of the board's battery-backed clock device is that it contains the backup battery
directly on the board. The battery is rated for a minimum of 6 years of clock and internal CMOS RAM
backup under conditions of no power to the board. The battery is removable for easy exchange with a
new type or replacement when the battery is exhausted.
The battery is a Digital-Logic AG replacement part: MS3V-BAT. The battery-backed clock can be set
using the Digital-Logic AG SETUP at boot-time.
RTC-Address MAP:
The onboard NiCd Battery with 220mAh capacity is able to work over 8 years without replacement.
The BQ3286 consumes the following currents:
Typical battery current at 25°C :
00 - 0F Real time clock
10 - 3F BIOS setup (Standard)
40 - 7F Extended BIOS or SuperState BIOS setup
0.3 µA max. 0.5 µA
23
MSM286 Manual V6.4