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

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READING THE CLOCK

When reading the RTC data, it is recommended to halt updates to the external set of double-buffered RTC

registers. This puts the external registers into a static state, allowing data to be read without register

values changing during the read process. Normal updates to the internal registers continue while in this

state. External updates are halted when a 1 is written into the read bit, B6 of the Control register (1FF8h).

As long as a 1 remains in the Control register read bit, updating is halted. After a halt is issued, the

registers reflect the RTC count (day, date, and time) that was current at the moment the halt command

was issued. Normal updates to the external set of registers resume within 1 second after the read bit is set

to 0 for a minimum of 500

s. The read bit must be 0 for a minimum of 500s to ensure the external

registers are updated.

SETTING THE CLOCK

The 8th bit, B7 of the Control register, is the write bit. Setting the write bit to 1, like the read bit, halts

updates to the DS1553 (1FF8h–1FFFh) registers. After setting the write bit to 1, RTC registers can be

loaded with the desired RTC count (day, date, and time) in 24-hour BCD format. Setting the write bit to 0

then transfers the values written to the internal RTC registers and allows normal operation to resume.

CLOCK ACCURACY (DIP MODULE)

The DS1553 is guaranteed to keep time accuracy to within

1 minute per month at +25C. The RTC is

calibrated at the factory by Dallas Semiconductor using nonvolatile tuning elements and does not require

additional calibration. For this reason, methods of field clock calibration are not available and not

necessary. The electrical environment also affects clock accuracy and caution should be taken to place the

RTC in the lowest level EMI section of the PC board layout. For additional information, refer to

Application Note 58: Crystal Considerations with Dallas Real-Time Clocks, available on our website at

www.maxim-ic.com/appnoteindex.com.

CLOCK ACCURACY (PowerCap MODULE)

The DS1553 and DS9034PCX are each individually tested for accuracy. Once mounted together, the

module typically keeps time accuracy to within

1.53 minutes per month (35ppm) at +25°C. The

electrical environment affects clock accuracy and caution should be taken to place the RTC in the lowest

level EMI section of the PC board layout. For additional information, refer to Application Note 58:

Crystal

Considerations

with

Dallas

Real-Time

Clocks,

available

on

our

website

at

www.maxim-ic.com/appnoteindex.com.

FREQUENCY TEST MODE

IRQ

/FT output toggles at 512Hz when the FT bit is 1, the Alarm Flag Enable bit (AE) is 0, and the

output and the frequency test mode can be used as a measure of the actual frequency of the 32.768kHz

operation. The FT bit is cleared to 0 on power-up.