The trend in semiconductor memory, as evidenced by presentations at last week’s International Solid State Circuits Conference, is towards applications-specific variants of the various widely-used types of memory chip. Texas Instruments Inc is at the forefront of the new trend, and presented two new memory chip developments, one to simplify the in-system reprogramming of electronic modules, and the other to enable system performance approaching maximum processor capability. The first of the new parts is an EPROM with a burst mode memory configuration, which in many system applications should enable performance approaching maximum processor capability. Up to now, microprocessor performance improvements have outpaced corresponding access time improvements in high-density semiconductor memories. One approach taken by designers has been to slow processor access to EPROM memory but this compromises system performance. Another alternative has been the use of costly, complex RAM caches using statics. Texas says its 1M-bit CMOS BurstMode EPROM is fast enough to allow direct EPROM access, eliminating the need for a program cache buffer, by virtue of its 20nS statistical access time, achieved by using a 1.4 micron lithography process. Texas sees the BurstMode EPROM being used in any application requiring rapid program memory access, including those with digital signal processors and RISC processor architectures. Flash EEPROM Texas Instruments’ other memory chip described at the Conference is a Flash EEPROM electrically erasable programmable read-only memory, and Texas is confident that 5 Volt Flash EEPROMs will be a major nonvolatile product technology in the 1990s. The devices offer the flexibility of in-system electrical alterability with the density and cheapness of current EPROMs. The Texas Flash EEPROM uses only one 5 Volt power supply for program, erasure and read operations but is claimed to offer performance and price comparable with dual power-supply Flash EEPROMs – 12V for programming and erase and 5V for the read operation. A 5V Flash EEPROM is the preferred solution for in-system write applications because no extra high-voltage, high-current power supply is required. Unlike EPROMs, Flash EEPROMS do not have to be removed from the system, and go through the process of having the contents erased by ultraviolet light before they can be reprogrammed using dedicated equipment. Instead, they can be erased electrically within a system, simplifying matters for the designer. Flash EEPROMs are expected to play a significant role in future systems because their in-system reprogrammability improves product development cycle time, increases manufacturing flexibility and allows remote program alteration, and could replace both EPROMs and EEPROMs in a variety of applications, including automotive systems, instrumentation and embedded controllers, Texas believes, as well as leading to the emergence of new applications, such as data cards and image storage.
