DS1553 datasheet(3/20 Pages) MAXIM

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DS1553 64kB, Nonvolatile, Year-2000-Compliant Timekeeping RAM

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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 ( IRQ /FT) and reset ( RST ) outputs that can be used to control CPU activity.

The IRQ /FT interrupt output can be used to generate an external interrupt when the RTC register values

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 IRQ /FT or RST outputs can also be used as a CPU watchdog timer. CPU

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 RST

output is used for this function.

The DS1553 also contains its own power-fail circuitry, which automatically deselects the device when the

VCC supply enters an out-of-tolerance condition. This feature provides a high degree of data security

during unpredictable system operation brought on by low VCC levels.

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

DS1553 Datasheet(PDF) 3 Page - Maxim Integrated Products