U631H64

a: Stresses greater than those listed under „Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress rating only, and functional operation of the device at condition above those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect reliability.

The U631H64 has two separate modes of operation: SRAM mode and nonvolatile mode. In SRAM mode, the memory operates as an ordinary static RAM. In nonvolatile operation, data is transferred in parallel from SRAM to EEPROM or from EEPROM to SRAM. In this mode SRAM functions of U631H64 are disabled.

The U631H64 is a fast static RAM (25, 35, 45 ns), with a nonvolatile electrically erasable PROM (EEPROM) element incorporated in each static memory cell. The SRAM can be read and written an  unlimited number of times, while independent nonvolatile data resides in EEPROM. Data transfers from the SRAM to the EEPROM (the STORE operation), or from the EEPROM to the SRAM (the RECALL operation) are initiated through software sequences. The U631H64 combines the high performance and ease of use of a fast SRAM with nonvolatile data integrity.

Once a STORE cycle U631H64 is initiated,further input or output are disabled until the cycle is completed.Because a sequence of addresses is used for STORE initiation, it is important that no other read or write accesses intervene in the sequence or the sequence will be aborted.

Internally, RECALL U631H64 is a two step procedure. First, the SRAM data is cleared and second, the nonvolatile information is transferred into the SRAM cells.The RECALL operation in no way alters the data in the EEPROM cells. The nonvolatile data can be recalled an unlimited number of times.