DS1553 Maxim, DS1553 Datasheet - Page 3

• Manufacturer Part Number: DS1553
• Description: The DS1553 is a full-function, year-2000-compliant (Y2KC) real-time clock/calendar (RTC) with an RTC alarm, watchdog timer, power-on reset, battery monitor, and "8k x 8 nonvolatile static RAM (NV SRAM)
• Manufacturer: Maxim

DETAILED DESCRIPTION
The RTC registers in the DS1553 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. Assuming the internal oscillator is turned on, the internal
set of registers is continuously updated. This occurs regardless of external registers settings to guarantee
that accurate RTC information is always maintained.
The DS1553 has interrupt (
The
match user-programmed alarm values. The interrupt is always available while the device is powered from
the system supply, and it can be programmed to occur when in the battery-backed state to serve as a
system wakeup. Either the
activity is monitored and an interrupt or reset output is activated if the correct activity is not detected
within programmed limits. The DS1553 power-on reset can be used to detect a system power-down or
failure and can hold the CPU in a safe reset state until normal power returns and stabilizes. The
output is used for this function.
The DS1553 also contains its own power-fail circuitry, which automatically deselects the device when the
V
during unpredictable system operation brought on by low V
PACKAGES
The DS1553 is available in a 28-pin DIP and a 34-pin PowerCap module. The 28-pin DIP module
integrates the crystal, lithium energy source, and silicon in one package. The 34-pin PowerCap module
board is designed with contacts for connection to a separate PowerCap (DS9034PCX) that contains the
crystal and battery. This design allows the PowerCap to be mounted on top of the DS1553P after
completion of the surface-mount process. Mounting the PowerCap after the surface-mount process
prevents damage to the crystal and battery due to the high temperatures required for solder reflow. The
PowerCap is keyed to prevent reverse insertion. The PowerCap module board and PowerCap are ordered
separately and shipped in separate containers. The part number for the PowerCap is DS9034PCX.
Figure 1. Block Diagram
CC
IRQ
supply enters an out-of-tolerance condition. This feature provides a high degree of data security
/FT interrupt output can be used to generate an external interrupt when the RTC register values
IRQ
IRQ
/FT) and reset (
/FT or
RST
outputs can also be used as a CPU watchdog timer. CPU
RST
3 of 20
) outputs that can be used to control CPU activity.
CC
levels.
RST