ROM – Read-Only Memory

Read-only memory (usually known by its acronym, ROM) is used in computers and other electronic devices to store programs and constant data. In Mask ROM, the data is physically encoded in the circuit, so it can only be programmed during fabrication. While Mask ROM are very economical in large quantities, there are some major disadvantages associated with the technology: The turnaround time between completing the data set for a Mask ROM and receiving the finished product is long and bugs lead to a long cycle time.

Subsequent developments addressed these problems and the invention of EPROM, or Erasable Programmable Read-Only Memory, solved the problems, because the memory content can be reset by exposure the silicon chip through a glass window in the housing to strong UV light. The same EPROM chip packaged into an opaque housing, results in the OTP-ROM, or One-time Programmable Read-Only Memory, a technology usually used for quick production ramp-up at higher costs. The development of the Flash Memory, a specific type of EEPROM (Electrically Erasable Programmable Read-Only Memory), allows changes in the programs or data on the fly and replaced Mask ROM in most applications.

Texas Instruments used Mask ROM both as program memory for calculators, for instance with the Solid State Software Modules of the TI-58/59 family and the program memory of the TI-81 graphing calculator, or as data memory of the Solid State Speech Modules of the Speak & Spell series. Other ROM intense applications are the Spell-Checker RR-1 and the Language Translator PS-5600.

In the 70s and early 80s Texas Instruments developed and manufactured their own Mask ROM while in the heyday of the Mask ROM – between the early 80s till mid 90s – Sharp Electronics Corp. of Japan dominated the market. Please find a list of Sharp Mask ROM located in some TI products here. In most products the layout of the printed circuit board (PCB) was designed in a way to accommodate both mask ROM and OTP-ROM. This allowed a faster market introduction and gained some flexibility for bug fixing in the program. We know for the TI-82 graphing calculators at least 12 different ROM-Versions since its introduction in 1993. Please find a list of OTP-ROM used in TI products here. In 1998 Texas Instruments introduced with the TI-73 the first graphing calculator based on Flash technology and most subsequent designs are based on this design. Please find a brief overview about Flash-ROM used in TI calculators here.

Mask ROM

EPROM

OTP-ROM

Flash-ROM (NOR Technology)

Spansion was founded in 1993 as a joint venture between AMD and Japan's Fujitsu Limited. AMD took control of the company in 2003 and spun it off as an independent maker of Flash-ROM chips in December 2005.

EON (Eon Silicon Solution, Inc.) is a fabless semiconductor company based in Hsin-Chu, Taiwan and focusing on non-volatile memory.

Flash-ROM (NAND Technology)