DS1556 1M, Nonvolatile, Y2K-Compliant Timekeeping RAM

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match user programmed alarm values. The interrupt is always available while the device is powered from

the system supply and can be programmed to occur when in the battery-backed state to serve as a system

wake-up. 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 will be activated if the correct activity is not detected within

programmed limits. The DS1556 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 DS1556 also contains its own power-fail circuitry, which automatically deselects the device when the

PACKAGES

The DS1556 is available in two packages (32-pin DIP and 34-pin PowerCap module). The 32-pin DIP

style module integrates the crystal, lithium energy source, and silicon all 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

DS1556P after the 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

Dallas

Semiconductor

DS1556