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Friday, December 23, 2011

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.

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