DS1687 Maxim, DS1687 Datasheet - Page 23

• Manufacturer Part Number: DS1687
• Description: The DS1685/DS1687 are real-time clocks (RTCs) designed as successors to the industry-standard DS1285,DS1385, DS1485, and DS1585 PC RTCs
• Manufacturer: Maxim

The RTC address is latched on the falling edge of the ALE signal. Each time an RTC address is latched, the
register address stack is pushed. The stack is only four registers deep, holding the three previous RTC addresses
in addition to the current RTC address being accessed. The following waveform illustrates how the BIOS could
recover the RTC address when an SMI occurs.
1) The RTC address is latched.
2) An SMI is generated before an RTC read or write occurs.
3) RTC address 0Ah is latched and the address from 1 is pushed to the RTC Address-1 stack location. This step
4) RTC address 4Eh is latched and the address from “1” is pushed to location “4Eh,” “RTC Address-2” while 0Ah
ALE
is necessary to change the bank select bit, DV0 = 1.
is pushed to the “RTC Address-1” location. The data in this register, 4Eh, is the RTC address lost due to the
SMI.
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DS1685/DS1687 3V/5V Real-Time Clocks
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