Electronic – Were mask ROMs with stock contents ever sold? or why not


To clarify: did any of the mask ROM or discrete IC vendors make and sell ROMS (or effective ROMs optimized by giant Karnaugh map) with fixed non-proprietary contents that could be used in building a circuit from stock, in addition to the normal custom ROMs.

A primary application would have been pre computed look-up-tables of really any common single-variable function.

For example:

  • A 64×8 ROM holding a quarter of a sine wave, or a "256×8" holding the full circle.
  • A ROM converting integer n to ln(n) and a companion converting fixed-point m to e^m.

There seem to be some 74-series chips that could be interpreted this way according to the listing on Wikipedia.

  • 74408 – 8-bit parity tree
  • 74630-35 – Error detection and correction chips

But these seem to be the exception rather than the rule and are likely to be much more efficient in practice.

If catalog stock ROMs were never sold why weren't they? What made them a bad fit for applications that could use them but couldn't justify custom silicon?

Best Answer

Character generator ROMs with 5x7 ASCII codes were certainly sold.

One example was the Signetics 2513, a rather nasty and sluggish P-MOS chip requiring three supply rails.

OTP and UV-erasable EPROMs came along not so long after- so the cost advantages of mask ROMs were not as significant as compared to mask charges (mask ROMs are not really fully custom silicon, only a metal layer was customized). Typical costs were low thousands of dollars and a MOQ in the thousands from US suppliers.

There were also small TTL OTP ROMs made with fuse technology.

And there were (and are) 4 and 8-bit micros pre-programmed for specific tasks, perhaps with an application-specific peripheral or two.