memory products - Al Kossow's Bitsavers

MK48Z02/12(B)-12/15/20/25DATA RETENTION MODEWith Vee applied, the MK48Z02112 operates as aconventional BYTEWIDE static ram. However, Veeis being constantly monitored. Should the supplyvoltage decay, the RAM will automatically powerfaildeselect, write protecting itself when Vee fallswithin the VpFD (max), VpFD (min) window. TheMK48Z02 has a VPFD (max) -VPFD (min) window of4.75 volts to 4.5 volts, providing very high data security,particularly when all of the other system componentsare specified to 5.0 volts plus and minus10%. The MK48Z12 has a VPFD (max) -VPFD (min)window of 4.5 volts to 4.2 volts, allowing users constrainedto a 10% power supply specification to usethe device.FIGURE 5. CHECKING THE BOK FLAG STATUSREAD DATAAT ANYADDRESSNote: A mid-write cycle power failure may corruptdata at the current address location, but does notjeopardize the rest of the RAM's content. At voltagesbelow VPFD (min), the user can be assured thememory will be in a write protected state, providedthe Vce fall time does not exceed tF. TheMK48Z02112 may respond to transient noise spikesthat reach into the deselect window if they shouldoccur during the time the device is sampling Vee.Therefore decoupling of power supply lines isrecommended.The power switching circuit connects external Veeto the RAM and disconnects the battery when Veerises above Vso. As Vee rises the battery voltageis checked. If the voltage is too low, an internal BatteryNot OK (BDK) flag will be set. The BOK flagcan be checked after power up. If the BOK flag isset, the first write attempted will be blocked. Theflag is automatically cleared after first write, and normalRA~ operation resumes. Figure 5 illustrateshow a B K check routine could be structured.Normal RAM operation can resume tREe after Veeexcee.!ls V.l!fD (Max). Caution should be taken tokeep E or W high as Vee rises past VPFD (Min) assome systems may perform inadvertent write cyclesafter Vee rises but before normal system operationbegins.WRITECOMPLIMENTDATA BACKTO SAMEADDRESSREAD DATAAT SAMEADDRESSAGAINWRITE ORIGINALDATA BACK TOSAME ADDRESSNOTIFY SYSTEMOF LOWeATTERY (DATA MAYBE CORRUPTED)5/11281