RTC address map

The address map of DS12887

• This has total of 128 bytes of RAM space with addresses 00-7Fh.
• The first 10 i.e. 00-09 are kept aside for RTC values of time, calendar and alarm data.
• The next 4 are control and status registers.
• The next 114 bytes from address 0E-7F are available for data storage.
• Register C and D are read only.
• The D7 of register A is read only.
• The high order bits of seconds byte are read only.

Address map

0 – 00h	Seconds
1 – 01h	Seconds alarm
2 – 02h	Minutes
3 – 03h	Minutes alarm
4 – 04h	Hours
5 – 05h	Hours alarm
6 – 06h	Day of week
7 – 07h	Day of month
8 – 08h	Month
9 – 09h	Year
10 – 0Ah	Register A
11 – 0Bh	Register B
12 – 0Ch	Register C
13 – 0Dh	Register D

Register A

UIP

DV2

DV1

DV0

RS3

RS2

RS1

RS0

UIP update in progress. This is a read only bit.

DV2 – 0

DV1 – 1

DV0 – 0

Will turn the oscillator on.

RS3,RS2,RS1,RS0 provides 14 different frequencies at the SQW pin.

Value of register a will remain as..

0

0

1

0

0

0

0

0

A = 20h

Register B

SET

PIE

AIE

UIE

SQWE

DM

24/12

DSE

SET	SET =0; clock is counting once per second and times and dates are updated. SET =1; update is inhibited(during initialization we must set SET=1)
PIE	Periodic interrupt enable
AIE	Alarm interrupt enable. The AIE=1 will allow the IRQ to be asserted, when all 3 bytes of time equals alarm bytes. In short will raise an interrupt when time equals alarm time.
UIE	Don’t know so see the datasheet.
SQWE	Square wave enable.
DM	Data mode. DM=0; for BCD data format. DM=1; for binary(hex) data format.
24/12	1 for 24 hour mode 0 for 12 hour mode
DSE	Daylight saving enable. 1 enables daylight saving(first Sunday in april and last Sunday in October) 0 disables daylight saving

 So we will keep the setting BCD data format. 24 hrs time, and daylight saving on.

Giving us the value of register.

1

0

0

0

0

0

1

1

B = 83h.

RTC DS12887 address location for time, calendar and alarm.

Address Location	Function	Decimal range	Binary(hex)	BCD
0	Seconds	0-59	00-3B	00-59
1	Seconds alarm	0-59	00-3B	00-59
2	Minutes	0-59	00-3B	00-59
3	Minutes alarm	0-59	00-3B	00-59
4	Hours, 12 hour mode	1-12	01-0C AM	01-12 AM
	Hours, 12 hour mode	1-12	81-8C PM	81-92 PM
	Hours, 24 hour mode	0-23	0-17	0-23
5	Hours alarm, 12 hour	1-12	01-0C AM	01-12 AM
	Hours alarm, 12 hour	1-12	81-8C PM	81-92 PM
	Hours alarm, 24 hour	0-23	0-17	0-23
6	Days of the week SUN=1	1-7	01-07	01-07
7	Day of the month	1-31	01-1F	01-31
8	Month	1-12	01-0C	01-12
9	Year	0-99	00-63	00-99

 one needs to remember above tables to write a program for RTC interfacing with 8051.