DS2417

1-WIRE CRC GENERATOR Figure 4

4 of 15

R

8TH

STAGE

7TH

STAGE

6TH

STAGE

S

2ND

STAGE

3RD

STAGE

4TH

STAGE

5TH

STAGE

1ST

STAGE

INPUT DATA

TIMEKEEPING

A 32.768kHz crystal oscillator is used as the time base for the real-time clock counter. The oscillator can

be turned on or off under software control. The oscillator must be on for the real-time clock to function.

The real-time clock counter is double buffered. This allows the master to read time without the data

changing while it is being read. To accomplish this, a snapshot of the counter data is transferred to a

read/write buffer, which the user accesses.

DEVICE CONTROL BYTE

The DS2417 can generate interrupt pulses to trigger activities that have to occur at regular intervals. The

selection of this interval and the on/off control of the 32.768kHz crystal oscillator are done through the

device control byte. This byte can be read and written through the Clock Function commands.

Device Control Byte

7

6

5

4

3

2

1

0

IE

IS2

IS1

IS0

OSC

OSC

0

0

Bit 0 - 1

0

No function

Bits 0 and 1 are hard-wired to read all 0’s.

Bit 2 - 3

OSC Oscillator Enable/Disable

These bits control/report whether the 32.768kHz crystal oscillator is running. If the oscillator is running,

both OSC bits will read 1. If the oscillator is turned off these bits will all read 0. When writing the

device control byte both occurrences of the OSC bit should have identical data. Otherwise, the value in

bit address 3 (bold) takes precedence.