DS1553 64kB, Nonvolatile, Year-2000-Compliant Timekeeping RAM
PIN DESCRIPTION
A0–A12
DQ0–DQ7
IRQ
/FT
RST
CE
OE
WE
- Address Input
- Data Input/Outputs
- Interrupt, Frequency Test Output
(Open Drain)
- Power-On Reset Output (Open Drain)
- Chip Enable
- Output Enable
- Write Enable
- Power-Supply Input
- Ground
- No Connection
V
CC
GND
N.C.
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
V
CC
supply enters an out-of-tolerance condition. This feature provides a high degree of data security
during unpredictable system operation brought on by low V
CC
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.
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DALLAS [ DALLAS SEMICONDUCTOR ]
