DS87C530_1 Datasheet, PDF (9/44 Pages) Dallas Semiconductor – EPROM/ROM Micro with Real Time Clock

REGISTER
PSW
WDCON
ACC
EIE
B
RTASS
RTAS
RTAM
RTAH
EIP
RTCC
RTCSS
RTCS
RTCM
RTCH
RTCD0
RTCD1
BIT 7
CY
SMOD_1
-
0
0
0
-
SSCE
0
0
BIT 6
AC
POR
-
0
0
0
-
SCE
0
0
BIT 5
F0
EPFI
ERTCI
0
PRTCI
MCE
BIT 4
RS1
PFI
EWDI
PWDI
HCE
BIT 3
RS0
WDIP
BIT 2
OV
WTRF
BIT 1
FL
EWT
EX5
EX4
EX3
PX5
PX4
PX3
RTCRE RTCWE RTCIF
DS87C530/DS83C530
BIT 0 ADDRESS
P
D0h
RWT
D8h
E0h
EX2
E8h
F0h
F2h
F3h
F4h
F5h
PX2
F8h
RTCE
F9h
FAh
FBh
FCh
FDh
FEh
FFh
NONVOLATILE FUNCTIONS
The DS87C530/DS83C530 provides two functions that are permanently powered if a user supplies an
external energy source. These are an on-chip Real Time Clock and a nonvolatile SRAM. The chip
contains all related functions and controls. The user must supply a backup source and a 32.768 kHz
timekeeping crystal.
REAL TIME CLOCK
The on-chip Real Time Clock (RTC) keeps time of day and calendar functions. Its time base is a 32.768
kHz crystal between pins RTCX1 and RTCX2. The RTC maintains time to 1/256 of a second. It also
allows a user to read (and write) seconds, minutes, hours, day of the week, and date. The clock
organization is shown in Figure 2.
Timekeeping registers allow easy access to commonly needed time values. For example, software can
simply check the elapsed number of minutes by reading one register. Alternately, it can read the complete
time of day, including subseconds, in only four registers. The calendar stores its data in binary form.
While this requires software translation, it allows complete flexibility as to the exact value. A user can
start the calendar with a variety of selections since it is simply a 16-bit binary number of days. This
number allows a total range of 179 years beginning from 0000.
The RTC features a programmable alarm condition. A user selects the alarm time. When the RTC reaches
the selected value, it sets a flag. This will cause an interrupt if enabled, even in Stop mode. The alarm
consists of a comparator that matches the user value against the RTC actual value. A user can select a
match for 1 or more of the sub-seconds, seconds, minutes, or hours. This allows an interrupt
automatically to occur once per second, once per minute, once per hour, or once per day. Enabling
interrupts with no match will generate an interrupt 256 times per second.
Software enables the timekeeper oscillator using the RTC Enable bit in the RTC Control register (F9h).
This starts the clock. It can disable the oscillator to preserve the life of the backup energy-source if
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