DS1747/DS1747P Y2K-Compliant, Nonvolatile Timekeeping RAMs

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Figure 1. Block Diagram

PACKAGES

The DS1747 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 Power-Cap to be mounted on

top of the DS1747P 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 DS1747 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 one is written into the read bit, bit 6 of the century register, see

Table 2. As long as a one 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 DS1747 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 zero. The READ bit must be set to a zero for a minimum of

500

ms to ensure the external registers will be updated.

Dallas

Semiconductor

DS1747