Specifications

PC/II+p Board Technical Reference Manual 60

7.21 Real-Time Clock

The PC/II+p contains an optional Real-Time Clock (RTC), a Dallas Semiconductor DS1685E. This clock is a

full-function part, and is certified as Year-2000 compliant by Dallas. The RTC uses a 32.768 KHz crystal and

a 3.0V Lithium battery. The battery is soldered onto the circuit board.

Information contained in the following sub-sections is presented in summary form. For more detailed

information about the Real-Time Clock, please refer to the DS1685E datasheet specified in section 2

"Reference Documents

" in this document.

7.21.1 Real-Time Clock – Features

• 242 Bytes battery backed up NVRAM

• RAM Clear input

• Low battery current (500 nA)

• Leap Year to year 2100 provides Year 2000 compliance

• Century byte with Automatic Rollover provides Year 2000 compliance

• 24 0r 12 Hour Format

• Programmable Alarm, Settable at Any Time hh:mm:ss, with Interrupt

• Programmable Timer, Settable to Periods Ranging from 122 uSec to 500 mSec

• Daylight Savings Time Support

• Unique 48-Bit Silicon Laser-Written Serial Number, Can be used by Customer Applications

The PC/II+p is factory-shipped with the Real-Time Clock set to the correct time and date for the default

North-American EST (Eastern Standard Time) time zone, or to the customer-specified time-zone. The

software for the Real-Time Clock is included in the system BIOS for boards containing the Real-Time Clock

option.

The Lithium battery is rated for 125 mAh (typical) in an operating range of -20C to +70C. Discharge current is

500 nA, and storage temperature is -40C to +60C.

7.21.2 Real-Time Clock – Setting Time and Date

The DOS clock is updated automatically by the Real-Time Clock upon Boot-Up. Should you change the time

or date in DOS, the PC/II+p will conversely update the Real-Time Clock hardware time and date. The

PC/II+p uses standard DOS instructions to change the time and date. If you are using standard DOS, and if

the time and date are displayed at boot time, you may at that point change the time and date if desired.

Standard DOS commands to change the TIME and DATE can also be used.

Time and date are also settable in most operating systems; please refer to the operating system

documentation for details.

7.21.3 Real-Time Clock – Using the NVRAM

The BIOS utilizes the battery backed up NVRAM to store its configuration information which it needs to

access at boot time and at other times. Besides the time and data information contained in the Real-Time

Clock hardware, the BIOS stores information about the Video preferences, floppy disk drive configuration,

and panel information.

A total of 114 Bytes of RAM in bank 0, and 128 Bytes of RAM in bank 1 are supported (total of 242 Bytes of

RAM).