EN87C196CB Datasheet, PDF (10/45 Pages) Maxim Integrated Products – EPROM/ROM Microcontrollers with Real-Time Clock

DS87C530/DS83C530 EPROM/ROM Microcontrollers with Real-Time Clock
Table 1. Special Function Register Locations (continued)
* Functions not present in the 80C52 are in bold.
REGISTER BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2
TL2
TH2
PSW
CY
AC
F0
RS1
RS0
OV
WDCON
SMOD_1 POR
EPFI
PFI
WDIF WTRF
ACC
EIE
—
—
ERTCI EWDI
EX5
EX4
B
RTASS
RTAS
0
0
RTAM
0
0
RTAH
0
0
0
EIP
—
—
PRTCI PWDI
PX5
PX4
RTCC
SSCE SCE MCE HCE RTCRE RTCWE
RTCSS
RTCS
0
0
RTCM
0
0
RTCH
RTCD0
RTCD1
BIT 1
FL
EWT
EX3
PX3
RTCIF
BIT 0
P
RWT
EX2
PX2
RTCE
ADDRESS
CCh
CDh
D0h
D8h
E0h
E8h
F0h
F2h
F3h
F4h
F5h
F8h
F9h
FAh
FBh
FCh
FDh
FEh
FFh
NONVOLATILE FUNCTIONS
The DS87C530/DS83C530 provide two functions that are permanently powered if a user supplies an
external energy source. These are an on-chip RTC and a nonvolatile SRAM. The chip contains all related
functions and controls. The user must supply a backup source and a 32.768kHz timekeeping crystal.
REAL-TIME CLOCK
The on-chip RTC keeps time of day and calendar functions. Its time base is a 32.768kHz 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. Figure 2 shows the clock organization.
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
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