DS1305

6 of 22

READING FROM THE CLOCK REGISTERS

Buffers are used to copy the time and date register at the beginning of a read. When reading in burst

mode, the user copy is static while the internal registers continue to increment.

Figure 2. RTC REGISTERS AND ADDRESS MAP

HEX ADDRESS

READ

WRITE

Bit7

Bit6

Bit5

Bit4

Bit3

Bit2

Bit1

Bit0

RANGE

00h

80h

0

10 Seconds

Seconds

00–59

01h

81h

0

10 Minutes

Minutes

00–59

P

01–12 + P/A

12

A

02h

82h

0

24

10

10 Hour

Hours

00–23

03h

83h

0

0

0

0

Day

1–7

04h

84h

0

0

10 Date

Date

1–31

05h

85h

0

0

10 Month

Month

01–12

06h

86h

10 Year

Year

00–99

—

—

Alarm 0

—

07h

87h

M

10 Seconds Alarm

Seconds Alarm

00–59

08h

88h

M

10 Minutes Alarm

Minutes Alarm

00–59

P

12

A

01–12 + P/A

09h

89h

M

24

10

10 Hour

Hour Alarm

00–23

0Ah

8Ah

M

0

0

0

Day Alarm

01–07

—

—

Alarm 1

—

0Bh

8Bh

M

10 Seconds Alarm

Seconds Alarm

00–59

0Ch

8Ch

M

10 Minutes Alarm

Minutes Alarm

00–59

P

12

A

01–12 + P/A

0Dh

8Dh

M

24

10

10 Hour

Hour Alarm

00–23

0Eh

8Eh

M

0

0

0

Day Alarm

01–07

0Fh

8Fh

Control Register

—

10h

90h

Status Register

—

11h

91h

Trickle Charger Register

—

12h–1Fh

92h–9Fh

Reserved

—

20h–7Fh

A0h–FFh

96 Bytes User RAM

00–FF

Note: Range for alarm registers does not include mask’m’ bits.

The DS1305 can be run in either 12-hour or 24-hour mode. Bit 6 of the hours register is defined as the

12- or 24-hour mode select bit. When high, the 12-hour mode is selected. In the 12-hour mode, bit 5 is the

AM/PM bit with logic high being PM. In the 24-hour mode, bit 5 is the second 10-hour bit (20 to 23

hours).

The DS1305 contains two time-of-day alarms. Time-of-day Alarm 0 can be set by writing to registers 87h

to 8Ah. Time-of-day Alarm 1 can be set by writing to registers 8Bh to 8Eh. The alarms can be

programmed (by the INTCN bit of the control register) to operate in two different modes; each alarm can

drive its own separate interrupt output or both alarms can drive a common interrupt output. Bit 7 of each

of the time-of-day alarm registers are mask bits (Table 2). When all of the mask bits are logic 0, a time-

of-day alarm only occurs once per week when the values stored in timekeeping registers 00h to 03h

match the values stored in the time-of-day alarm registers. An alarm is generated every day when bit 7 of

the day alarm register is set to a logic 1. An alarm is generated every hour when bit 7 of the day and hour

alarm registers is set to a logic 1. Similarly, an alarm is generated every minute when bit 7 of the day,