Mostek Calculator Integrated Circuits

Mostek Corporation was founded in 1969 as a spin-off of Texas Instruments and engaged in the manufacturing and marketing of Metal Oxide Semiconductors and Large Scale Integration (MOS/LSI) integrated circuits. Already in May 1970, Mostek started the development of the MK6010, the world's first "single-chip" calculator circuit for Nippon Calculating Machine Company, better known under their brand Busicom. The MK6010 –announced in November 1970 - was used in Busicom's first handheld calculator, the Handy LE-120A. Introduced in February 1971, it was the World's smallest handheld calculator and it kept this trophy for at least another year. 

Texas Instruments announced the "TMS1802 calculator-on-a-chip" in September 17, 1971, about one year later Mostek introduced the MK5020P, an improved but pin-compatible calculator chip. Not only did Mostek attract the attention of the electronic community, but they also attracted the attention of major consumers of MOS circuits and the company began an important relationship with Hewlett-Packard as one of the leading supplier of integrated circuits for HP's scientific calculators. Hewlett-Packard soon became Mostek's largest customer. In addition, Mostek's memory production was on the way to making it the world's leading RAM supplier.

Find a list of all known Texas Instruments calculator chips here.

The Part Numbering System of Mostek gives us immediately an idea if a calculator chip was a custom design (MK6nnn/nnnnn) or a catalog device (MK5nnn/nnnn):

Thank you to Jim Garrett and Frank Boehm!

First "single chip" calculator circuit

These chips are manufactured in a high-threshold, p-channel MOS process and using Dual-Inline-Ceramic (CDIP) packages with 40 pins.
The MK6010 did not include keyboard encoding, keyboard debouncing, clock generator or the display drivers. It operates from unusual voltages of -12V and -24V.

Early BASIC calculator chips

These chips are manufactured in an ion-implantation, depletion-mode load, P-channel MOS process and using Dual-Inline-Ceramic (CDIP) packages with 28 pins.

Later BASIC calculator chips

Enhanced chips with partly integrated display drivers and more functions and using Dual-Inline-Ceramic (CDIP) or Plastic (DIP) packages with 28 pins. 

Chipset for scientific and financial calculators

With the MK50075 Mostek created a novel architecture for scientific and financial calculators using external ROM circuits (read only memory). 

Calculator chips manufactured for Hewlett-Packard

Custom specific designs. 

Thanks to Eric Smith.

Other customized non-calculator chips

These chips are manufactured in a high-threshold, p-channel MOS process and using Dual-Inline-Ceramic (CDIP) packages with 24 to 40 pins.

Mostek Part Numbering System

Mostek introduced already with their first Integrated Circuits (ICs) a well-organized numbering scheme for their products. The leading M represents Mostek and the following one or two letters define the Product Status:

The Product Status is followed by the Product Group, originally a one-digit number but later having ROM components included in Group 3, isolating Group 38:

The Product Group is followed by the Product Number, in many cases a sequential number. Originally only 3-digit numbers, later expanded to 4 digits for many Product Groups but shortened to 2 digits for MK38nn CPU:

Additional fields are reserved for Revision (one character, starting with A) and Functional Classification (one character, L for Low-power).

The next field is used for the Package Type (one or two characters):

An additional field, the so-called Dash Number, with one or two numerical characters is used for Quality Grade, Custom Codes, Speed Classification, etc.

A typical single-chip calculator circuit from Mostek manufactured in 1975 might read MOSTEK MK50312N-1 ASSB. MALAYSIA 7535R: