DS1305

6 of 21

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

—

12–1FH

92–9FH

Reserved

—

20–7FH

A0–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 1). 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,

hour, and minute alarm registers is set to a logic 1. When bit 7 of the day, hour, minute, and seconds

alarm registers is set to a logic 1, alarm occurs every second.