DS1994

7 of 22

3

RTE

Real-time clock alarm flag

4

ITE

Interval timer alarm flag

5

CCE

Cycle counter alarm flag

Writing any of the interrupt enable bits to a logic 0 allows an interrupt condition to be generated when its

corresponding alarm flag is set (see the Interrupts section).

Control Register

7

6543

2

1

0

DSEL

STOP

START

AUTO

MAN.

OSC

RO

WPC

WPI

WPR

0201h

0

WPR Write protect real-time clock/alarms registers

1

WPI

Write protect interval timer/alarms registers

2

WPC Write protect cycle counter/alarms registers

Setting a write protect bit to a logic 1 permanently write protects the corresponding counter and alarm

registers, all write protect bits, and additional bits in the control register. The write protect bits cannot be

written in a normal manner (see the Write Protect/Programmable Expiration section).

3

RO

Read only

If a programmable expiration occurs and the read only bit is set to a logic 1, then the DS1994 becomes

read only. If a programmable expiration occurs and the read only bit is a logic 0, then only the 64-bit

lasered ROM can be accessed (see the Write Protect/Programmable Expiration section).

4

OSC

Oscillator enable

This bit controls the crystal oscillator. When set to a logic 1, the oscillator starts operation. When the

oscillator bit is a logic 0, the oscillator stops.

5

AUTO/MAN

Automatic/Manual Mode

When this bit is set to a logic 1, the interval timer is in automatic mode. In this mode, the interval timer is

enabled by the data line. When this bit is set to a logic 0, the interval timer is in manual mode. In this

mode, the interval timer is enabled by the STOP/START bit.

6 STOP/START

Stop/Start (in manual mode)

If the interval timer is in manual mode, the interval timer starts counting when this bit is set to a logic 0

and stops counting when set to a logic 1. If the interval timer is in automatic mode, this bit has no effect.