DS1500/DS1510
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PIN DESCRIPTION
VCCI
- Supply Voltage
A0-A4
- Address Inputs
DQ0-DQ7
- Data I/O
CS
- RTC Chip Select Input
OE
- RTC Output Enable Input
WE
- RTC Write Enable Input
IRQ
- Interrupt Output (open drain)
PWR
- Power-On Output (open drain)
RST
- Reset Output (open drain)
KS
- Kickstart Input
SQW
- Square wave output
VBAT
- Backup Battery Supply
VBAUX
- Auxiliary Battery Supply
CEI
- RAM Chip Enable Input
CEO
- RAM Chip Enable Output
VCCO
- RAM Power Supply Output
X1, X2
- 32.768 kHz Crystal pins
GND
- Ground
DESCRIPTION
The DS1500/DS1510 is a full function, year 2000 compliant, real-time clock/calendar (RTC) with an
alarm, watchdog timer, power-on reset, battery monitors, 256 bytes of on board non-volatile static RAM,
NV control for backing up an external SRAM, and a 32.768 kHz output. User access to all registers
within the DS1500/DS1510 is accomplished with a bytewide interface as shown in Figure 1. The RTC
registers contain century, year, month, date, day, hours, minutes, and seconds data in 24-hour BCD
format. Corrections for day of month and leap year are made automatically.
The RTC registers are double buffered into an internal and external set. The user has direct access to the
external set. Clock/calendar updates to the external set of registers can be disabled and enabled to allow
the user to access static data. When the crystal oscillator is turned on, the internal set of registers are
continuously updated; this occurs regardless of external register settings to guarantee that accurate RTC
information is always maintained.
The DS1500/DS1510 contains its own power fail circuitry which automatically deselects the device when
the VCCI supply falls below a power fail trip point. This feature provides a high degree of data security
during unpredictable system operation brought on by low VCCI levels. An external SRAM can be made
nonvolatile by using the VCCO and CEO pins. Nonvolatile control of the external SRAM is analogous to
that of the real-time clock registers. When VCCI slews down during a power fail, CEO is driven to an
inactive level regardless of CEI . This write protection occurs when VCCI is less than the power fails trip
point.
The DS1500/DS1510 has interrupt ( IRQ ), power control ( PWR ), and reset ( RST ) outputs which can be
used to control CPU activity. The IRQ interrupt or RST outputs can be invoked as the result of a time of
day alarm, CPU watchdog alarm, or a kick start signal. The DS1500/1511 power control circuitry allows
the system to be powered on via an external stimulus, such as a keyboard or by a time and date (wake-up)
alarm. The PWR output pin can be triggered by one or either of these events, and can be used to turn on
an external power supply. The PWR pin is under software control, so that when a task is complete, the
system power can then be shut down. The DS1500/DS1510 power-on reset can be used to detect a
system power down or failure and hold the CPU in a safe reset state until normal power returns and
stabilizes; the RST output is used for this function.
The DS1500 is a clock/calendar chip with the features described above. An external crystal and battery
are the only components required to maintain time-of-day and memory status in the absence of power.
The DS1510 incorporates the DS1500 chip, a 32.768 kHz crystal, and a lithium battery in a complete,
self-contained timekeeping module. The entire unit is designed by Dallas Semiconductor to provide a
minimum of 10 years of timekeeping and data retention in the absence of VCCI is guaranteed.