DS1305

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RTC AND RAM ADDRESS MAP

The address map for the RTC and RAM registers of the DS1305 is shown in Figure 2. Data is written to

the RTC by writing to address locations 80h to 9Fh and is written to the RAM by writing to address

locations A0h to FFh. RTC data is read by reading address locations 00h to 1Fh and RAM data is read by

reading address locations 20h to 7Fh.

ADDRESS MAP Figure 2

00H

1FH

CLOCK/CALENDAR

READ ADDRESSES ONLY

20H

7FH

96-BYTES USER RAM

READ ADDRESSES ONLY

80H

9FH

CLOCK/CALENDAR

WRITE ADDRESSES ONLY

A0H

FFH

96-BYTES USER RAM

WRITE ADDRESSES ONLY

CLOCK, CALENDAR AND ALARM

The time and calendar information is obtained by reading the appropriate register bytes. The real time

clock registers are illustrated in Figure 3. The time, calendar and alarm are set or initialized by writing

the appropriate register bytes.

Note that some bits are set to zero.

These bits will always read 0

regardless of how they are written. Also note that registers 12h to 1Fh (read) and registers 92h to 9Fh are

reserved. These registers will always read 0 regardless of how they are written. The contents of the time,

calendar and alarm registers are in the binary-coded decimal (BCD) format.

Please note that the initial power on state of all registers in not defined. Therefore it is important to

enable the oscillator (EOSC = 0) and disable write protect (WP = 0) during initial configuration.