DS1744 Datasheet, PDF (3/18 Pages) Dallas Semiconductor – Y2K-Compliant, Nonvolatile Timekeeping RAMs

Figure 1. Block Diagram
DS1744/DS1744P Y2K-Compliant, Nonvolatile Timekeeping RAMs
PACKAGES
The DS1744 is available in two packages (28-pin DIP and 34-pin PowerCap module). The 28-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
DS1744P 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.
CLOCK OPERATIONS—READING THE CLOCK
While the double-buffered register structure reduces the chance of reading incorrect data, internal updates
to the DS1744 clock registers should be halted before clock data is read to prevent reading of data in
transition. However, halting the internal clock register updating process does not affect clock accuracy.
Updating is halted when a 1 is written into the read bit, bit 6 of the century register (Table 2). As long as a
1 remains in that position, updating is halted. After a halt is issued, the registers reflect the count, that is,
day, date, and time that was current at the moment the halt command was issued. However, the internal
clock registers of the double-buffered system continue to update so that the clock accuracy is not affected
by the access of data. All the DS1744 registers are updated simultaneously after the internal clock-register
updating process has been re-enabled. Updating is within a second after the read bit is written to 0. The
READ bit must be a 0 for a minimal of 500ms to ensure the external registers are updated.
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