DS1213B

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OPERATION

The DS1213B SmartSocket performs five circuit functions required to battery back up a CMOS memory.

greater. The switch has a voltage drop of less than 0.2 volts.

enable.

The third function, write protection, is accomplished by holding the RAM chip enable signal to within 0.2

time power fail detection occurs, write protection is delayed until after the current memory cycle is

complete to avoid corruption of data. Power fail detection occurs in the range of 4.75 to 4.5 volts. During

nominal power supply conditions the chip enable signal will be passed through from the socket pin to the

socket contact with a maximum propagation delay of 20 ns.

The fourth function the DS1213B performs is to check battery status to warn of potential data loss. Each

comparator. If the battery supply is less than 2.0 volts, the second memory access to the SmartSocket is

inhibited. Battery status can, therefore, be determined by a three-step process. First, a read cycle is

performed to any location in the memory, in order to save the contents of that location. A subsequent

write cycle can then be executed to the same memory location, altering the data. If the next read cycle

fails to verify the written data, then the battery voltage is less than 2.0V and data is in danger of being

corrupted.

The fifth function the SmartSocket provides is battery redundancy. In many applications, data integrity is

paramount. In these applications it is desirable to use two batteries to ensure reliability. The DS1213B

SmartSocket provides two batteries and an internal isolation switch to select between them. During

battery back up, the battery with the highest voltage is selected for use. If one battery fails, the other

automatically takes over. The switch between batteries is transparent to the user. A battery status warning

will occur if both batteries are less than 2.0 volts. Each of the two internal lithium cells has a 45 mAh

capacity.

NOTE:

be present on socket contacts 28, 26 and 20.