Maxim DS87C530 Clock User Manual


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DS87C530/DS83C530 EPROM/ROM Microcontrollers with Real-Time Clock
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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 BIT 1 BIT 0 ADDRESS
TL2 CCh
TH2 CDh
PSW CY AC F0 RS1 RS0 OV FL P D0h
WDCON
SMOD_1
POR EPFI PFI WDIF WTRF EWT RWT
D8h
ACC E0h
EIE
— —
ERTCI EWDI EX5 EX4 EX3 EX2
E8h
B F0h
RTASS
F2h
RTAS
0 0 F3h
RTAM
0 0 F4h
RTAH
0 0 0 F5h
EIP
— —
PRTCI PWDI PX5 PX4 PX3 PX2
F8h
RTCC SSCE SCE MCE HCE RTCRE RTCWE RTCIF RTCE
F9h
RTCSS
FAh
RTCS
0 0 FBh
RTCM
0 0 FCh
RTCH
FDh
RTCD0
FEh
RTCD1
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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